So with laptops in order of cpu speed they are in this relative order (for simplicity sake I am ignoring AMD, if you want to ask questions about AMD I will gladly answer, the problem with AMD is they have so little of the market and thus it is hard to find systems I can recommend with fervor.)
intel i3 sandybridge
intel i3 ivybridge
intel i5 sandybridge
intel i5 ivybridge
intel i7 sandybridge
intel i7 ivybridge
All the laptop i3s and i5s are 2 cores 4 threads. i7s with qm are 4 cores 8 threads, i7 with m or u in the name are 2 cores 4 threads.
All core i3, i5, and i7 are the same chip underneath it all, the difference between them is the ghz speed they run at (and the amount of cache they have but ignore cache for it has a negligable impact.)
To get an idea of relative speeds here you go
Sandybridge i3-2350m (2.3ghz base) is 100
Ivybridge i3-3210m (2.4 ghz base) is 115
Sandybridge i5-2450m (2.5 ghz base, 3.1 ghz turbo) is 135
Ivybridge i5-3210m (2.5 ghz base, 3.1 ghz turbo) is 145
The i7 laptop chips that have the qm are quad cores (qm stands for quad core mobile). Unless you are doing more than 4 intensive things at one time and taking advantage of 4 threads they perform very similarly to a i5 dual core. If you can take advantage of all 4 cores / 8 threads at a time they are twice as fast as the i5 dual core but if you are not taking advantage of those 2 cores / 4 threads you are literally wasting money. For what you are describing it sounds like a i5 would be best for you for you describe nothing that would take advantage of a i7. If you were doing video editing or compiling I would be trying to get you an intel i7 but for normal use an i5 is fast enough. With qm think workstation/desktop replacement if you are not doing these tasks you are wasting money.
As you can see the difference between sandybridge and ivybridge is not much about 6 to 10% due to slight tweaks, and sometimes 100 mhz faster which is 5% on the clock speed. The difference between the i3 and i5 is about 30% faster single and dual threaded performance due to turbo boost boosting the ghz from 2.3 to 2.5 ish to about 3 ghz.
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The reason why to get ivybridge is due to the better graphics. Intel hd3000 graphics on sandybridge is perfectly adequate for office and hd video watching, but if you want to game I would recommend getting a dedicated video card. Intel hd4000 is a slightly decent integrated graphics in a pinch but if you want to game I would recommend going all the way to dedicated card such as nvidia gt540m, gt630m (renamed gt540m), gt640m le, gt 650m, gtx 660m (double the speed of a 540m). If you get a dedicated card make sure it supports optimus so you can get drivers directly from nvidia instead of the oem (dell, hp, sony, etc.) Stay away from anything with dedicated radeon for getting drivers for these cards is a pain in the ass since you almost always get drivers from the oem directly. This may change in the future but currently it sucks ass (see the recent anandtech comments on enduro for more information.)
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There is almost no difference in battery life between sandybride vs ivybridge of the same voltage. 30 mins more at max. What ivybridge with their tri gate transistors ("3d" transistors") allow is their ultra low voltage chips to have almost the same mhz as their full voltage chips. Because of this in a 13 inch ultrabook you can get almost the same mhz as their traditional 15" size laptop. For example the i5 3317u is an ultrabook i5 that has a 1.7 ghz speed and a 2.6 ghz max turbo boost. The i5 3210m is a tradional i5 that is 2.5 ghz speed and 3.1 ghz max turbo boost, for having a max power consumption that is double (35w) the 3210m is only 20% faster than the 3317u which has a max power consumption of 17w. (to go back to those relative scores we are talking about the i5 3317u is roughly 125 vs 145 for the i5 3210m)
What determines battery life is not max power consumption but idle power consumption. And since sandybridge and ivybridge have a similar idle power consumption you barely get any more battery life with ivybridge.
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What will make the laptop feel much faster is getting a solid state drive in it. An i3 with a solid state drive will feel faster with a ssd than i7 with no ssd unless you are doing video rendering. Everything will load instantly with an ssd.
Almost all laptops can have their harddrive switched with a 7mm ssd or a 9mm. This will void the warranty though. If there is only 1 slot though you will have to take out the mechanical hard drive. If it is a 17 inch it may have two 2.5 inch bays so you can do 1 ssd and mechanical drive (some big 15 inches allow this). If the computer has a dvd drive you can buy adapters allowing you to take out the dvd drive and putting an ssd in its place. If you get a 2.5" ssd and do it yourself get a samsung 830 or a crucial ssd, an intel would be my third choice.
Some of these new computers have a slot called msata which is a new size for ssds. You can have a small computer which has space for a 2.5" hard drive and still have a slot for a msata ssd. An msata ssd is about 1/4 the physical size of a 2.5" hard drive. Some manufactures have properitary msata slots (ASUS comes to mind) so make sure that brand works with that drive. (Crucial msata ssds seem to be a good bargain on price for the do it yourselfer, I know the samsungs exist but they are hard to find on the market.)
Intel Ultrabooks are new computers in the 11 to 14" size that have ssds or ssds+hard drives in a combo form. These maybe what you want if you want to get a prebuilt laptop with changing parts. Some 14" ultrabooks have dvd drives but most are going for as light as possible. They start off in the $600 price for an onsale ultrabook but the normal starting price is about $800
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We were asking about screens for if you are going to be working for extended periods of time with a laptop the screen quality is one of the most important parts of the laptop experience. Some laptops have horrible screens, some are decent it is really hit or miss. There are many nice sony and hp with ips screens in the 15 inch size and the asus zenbook 13" ultrabooks with ips screens. A Sony with IPS 1080p screen is much better than a cheap 1080p screen, and is night and day with the super cheap 768p screens.
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Brands
For brands in the value section acer is alright as long as you do not get anything with the floating island keyboard garbage. (Aka the acer timeline x and acer v3 and v5 series are alright.)
For quality try to stick with asus, sony, or lenovo thinkpad they will cost more. (Lenovo ideapads are not the same thing as Lenovo thinkpads.)
I would stay away from HP. I am personally not a fan of toshiba being completely unimpressed. There are some nice Samsungs out there but there cheaper ones are not anything special.
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If you have more questions please ask and I will try my best to answer them.
I was unclear what size you want. Your son has a 15" dell is that an okay size for you, or is it not an okay size for you?
Do you mine adding an ssd to the computer yourself or you want it prebuilt from the factory they way you want it.
With a little more info I can start recommending computers.
I guess a price range would be appropriate. I'd like to stay well below a grand if at all possible. Discrete video card would be nice.
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