Yes, I just noticed that disabling hardware acceleration helped significantly. I picked a random Slashdot news article and scrolled from top to bottom, keeping the down arrow pressed down. With hardware "acceleration" enabled, it took 22 seconds. Without it, 9 seconds. A very unscientific benchmark for sure, but it reflects the impression I got. Without the hardware acceleration the speed seems to be about the same as with older FF3.
After getting disappointed by FF4, I installed Chrome. It seems even a bit snappier than any of the FF versions I've used.
I'm using a Nokia Booklet 3G laptop with Win7. Granted, it's not a particularly fast computer, but it has been sufficient for my web browsing needs with FF3. My main gripe with FF4 is that if the browser is indeed slower with hardware acceleration enabled, FF4 shouldn't enable it by default. Yes, technically enabled folks can tweak the settings to make the browser faster, but tweaking the settings SHOULDN'T be necessary for the average user.