What machine do you have where you cannot afford 30$ to put a 256MB DIMM in that thing? I added 256MB to get 352MB into my 8600 and MacOS X 10.0.4 was much more acceptable to me, and 10.1 is pretty good. I think some people have to get over the fact that X will NEVER be as fast as 9. All that fancy stuff doesn't even really have an impact on speed (most of the time, the shrinking effects/etc. do have a good impact on speed).
Since X is pre-emptively multitasked, there is NO WAY for an app to hog 100% of the CPU. This leads to the fact of it feeling a little more sluggish than before, especially when you have quite a few processes actively running.
Now on the topic of stuff being unloaded onto the GPU I can say this: YES IT IS! I am currently writing Voodoo drivers for X and I can say that if you EVER BOTHER to look at the source for Darwin, there is quite a bit of stuff being unloaded. However, there are certain things that cannot be unloaded EASILY. One of these is live resizing. This is because the GPU needs the pixels for the newly uncovered regions. This means MacOS X has to call the app to get the pixels, and the pass those pixels to the GPU. This takes time, and with all these high-res monitors, it REALLY chugs time. Pixel pushing usually takes 50% of any graphics operation, and live resizing requires a lot of it. Window moving is easier since you can push the revealed pixels onto the card, and have the card blit the window to the new location (screen->screen blits take only the time required to tell the card the operation) rather than push a whole new window pixmap onto the card.
I have run Linux with V3 acceleration in XWin, and have the sluggishness with live resizing that every other iMac user complains about. Everything else is okay but live resizing. The sluggishness IS NOT NEW.
Heck, the GForce 3, and the Rage Pro series of cards finally got ANY SORT OF 2D/3D acceleration support in 10.1 and there are still are non-ATi/NVidia cards that don't have driver support.
The only reason why G4 users get good resizing is because of the fact that vector units like Altivec make live resizing a more realistic possibility. Linux on a PC with MMX or any other vector unit gets decent live resizing, but since G3s and earlier don't have a vector unit, it is difficult to push so many pixels around.
No offense to anyone, just clearing the smoke.