Not really credible? WOW.... You've got blinders on.
80% of the office computers at the non-profit where I volunteer are still Pentium 4 powered. They run modern tasks on a daily basis -- it is how they get donations and survive.
Most office workers don't watch HD videos when they're supposed to be working. Those P4's run the database software and office suites on Windows 7 just fine.
I just can't believe all the elitist crap I hear on this forum. Some of you really sound like snobs -- Look at the hard facts... 25% of the world's computers are still running freakin' XP (and XP actually just increased in share in June).... At least these guys at the non-profit are running Win 7. There are a ton of non-profits that are using donated desktops that are around 5 - 10 years old. It's not like a computer suddenly stops running applications the day it turns 2 years old.
The average business uses a desktop for 4 years -- and many donate them to be used at non-profits (or recycled) after that. The catholic school down the street is running Pentium 3's in its computer lab. Seriously get a grip...... Modern tasks -- lol.
Because they are still functional and plentiful, people still use Pentium 4s. This fact is not in dispute. But to say that a Haswell and Pentium 4 would be indistinguishable from one another if the P4 had an SSD (and, presumably, at least a SATA 2 interface to host it) is difficult to swallow.
There are a lot of P4s out there. If you are stuck on an early Willamette, for example, then yes, you are going to feel the pain even if you somehow get past the harddrive bottleneck. A 3.4 ghz P4c would be much snappier, and I'm sure one of those with an SSD would be tolerable, especially if it also had 2 or more gigs of RAM.
I have used some old P4 workhorses recently. Most of them were hardly top-of-the-line when they were first sold. Yes, the harddrives on those machines certainly seem to hold them back, but there are scenarios where the machines clearly struggle for other reasons. One of those reasons is that the amount of RAM is too small (which exacerbates the harddrive problem). There are other I/O problems related to the chipset (memory controller is off-die, the system is limited by FSB throughput, blah blah blah). Isolating problems specific to the CPU being old and slow is difficult when there is so much else wrong.
Nobody is trying to suggest that a bunch of schools, churches, and charities should go out and buy Haswell quads (or hex/octocores!) for email and web browsing.
But please, don't tell me that some random Dell workhorse from 2002-2004 with an SSD shoehorned in there (somehow) is going to trade blows with a Haswell quad with a WD Black or . . . something along those lines. That Haswell machine will probably have 8 gigs of RAM and won't swap as aggressively. Even with an SSD, the P4 is going to be swap city if it's running Win7 or XP, especially if it's loaded down with as many background apps as the last P4 I saw was. Two different virus scanners/monitors. Ugh.
Sure, that P4 CAN run "modern tasks", but you'll feel the pain, especially once you hit some site full of Flash nonsense.
edit: OS load times don't tell the entire story. Also, how many of those donated P4s are 775 machines? 478 (or older) is going to be much more common in the cheap-as-in-free bin.