At least that is my experience with a recent (~1.5 years old) 1920x1200 TFT monitor. 1024x768 works fine, but at 1920x1200 the image gets really ugly.
There's also something about apple adapters, from what I heard they depend on some specific capabilities of the GPU only found in apple products, i.e. they don't work anywhere else. Not sure though, I never tried.
You're right about eyefinity: no server-side Xinerama, acceleration across all monitors without trouble. If eyefinity is fully supported, that is - I haven't used more than 2 monitors so far.
There's only two solution to have >=3 monitors without Xinerama: get a card with enough outputs (eyefinity) or get a matrox triplehead2go (you could call it a dvi splitter).