Works fine with my DVI screen (don't have HDMI to try though, and I never tried VGA for that matter either). I did have to make sure radeon was loading before kdm, otherwise I would get no signal.
With the latest kernel and xorg-edgers packages (probably the latest gits) 2D is very choppy. Firefox is unusable, Konqueror runs quite good, but overall 2D is much worse then without KMS.
I have KMS enabled for months now (9550 Radeon card), and I have to say I'm quite satisfied: desktop effects are working almost perfect, watching videos is excellent, my brother even plays Counter Strike, smaller memory footprint is also a benefit... Of course, I compile xf86-video-ati driver and mesa stack every once in a while from git.
The 9550 is quite an old card (I hasten to add I ran one happily using radeonhd across multiple installed distros until quite recently, because it simply can't cut the mustard for modern pc gaming)
The question is, what does this new driver do for more recent ati products? If anything...
Same here. I have 4 systems using self-compiled 2.6.33 kernels, xf86-video-ati, mesa and libdrm from git on Slackware systems and everything works fine with RS780 and RS420 chips, compositing desktop and video work quite well.
I don't use 3D softs so I don't know if there's any difference, probably a hit from DRI2 as far as I understood.
For all uses apart from 3D games and software, it's perfectly usable.
But I suppose this has to do with the version of libdrm and mesa shipped by the distros.
KMS kills 2D performance all across the board. However, it's not that bad with older chips (my 9800pro and 200m for example, and I would guess any pre r5xx chip as well); with those it remains rather usable. With my hd4850 KMS really screws things up (I will assume it's the same for any r6/7xx chip) as it is much much slower than UMS and certain applications are just unusable (Firefox being one).