I can't comment much on AMD mobile processors, but from what I've heard in general, an AMD is slightly slower than an Intel Core 2 clock-for-clock, which puts it moderately slower than an i3, i5, or i7 at the same clock speed. AMDs also tend to get slightly worse battery life, too. The AMDs should still have plenty of power for day-to-day tasks, though.
This is absolutely right, but only for the Athlon X2 and Turion X2 processors. The ones you see now everywhere have Athlon II (Athlon II, not just Athlon) X2 and Turion II X2 processors. These go clock-for-clock with Core 2 Duo processors. And the integrated graphics that come with these II series processors are far superior to Intel's integrated graphics.
Battery life has also improved with the II series, thank God, and with my girlfriend's new 2.2GHz Turion II M500 HP laptop I get 4.0 hours of battery life if I don't play video games or run DVDs most of the time. Mostly just internet use, video watching, Office type tasks, chatting, Skype. With the 2.0GHz Athlon II M300 you should get more battery life, as the Turion II's are faster and a little more power hungry.
Intel's i3, i5, and i7 are faster than AMD's current laptop offerings, so if you want to go really high-end, get an Intel laptop. But don't forget, get a discrete graphics card, because if you have an Intel IGP, even if you have a mobile i7 processor, you won't be doing any gaming sadly.
I'd recommend the ATi Radeon 5000 series (it does DX11, the 4000 series only does DX10.1 and is in general slower, but is still nice) or Nvidia GeForce GTX260m or another GTX200 series mobile card.
Anyway, yeah, not a huge fan of the old K8-based TL, QL, TK, RM series Athlon/Turion processors. Slower than Core 2 Duos, worse battery life... better graphics, sure, but that's about it. These new ones though are fantastic in my experience. The M500 gets a 5.7 in the Windows Experience Index, out of Windows 7's possible 7.9. Should be faster than an Intel Core 2 Duo T6600 by what I read online although I have not benched them against each other. On a platform basis, the M500 is clearly superior on a graphics standpoint, but if you're getting a discrete graphics card then who cares.
Never been a huge fan of Dell since 2003 or so when I started working on laptops, but I have such a bad taste in my mouth, I haven't played with them recently. Maybe they have improved. I do love HP, Toshiba, ASUS, and Compaq right now though.