As much as I'm hoping that TTM/GEM and KMS are nearly bug-free (since this means that they can get to the R600/R700 code sooner - and I'm in desperate need of it since I've been "reduced" to using the radeon driver for my HD4870), I'm thinking this is not quite the case. In fact, I'll be pleasantly surprised if by the time Fedora 12 and Ubuntu 9.10 come out, we have a fully functioning R600/R700 driver (never mind the speed of the thing, I'm just talking feature parity to the R500 cards).
off-topic, but still relevant (and no, it's not intended as a flame, I would like a serious answer to this, from someone working at AMD if possible):
Seriously, what the hell is happening at AMD over there? They rip out support for older cards, so I think "finally, my HD4870 will work smoothly on my ubuntu 9.04 system". Apparently not: the 9.5 fglrx driver is so riddled with performance regressions when bundled with X.org latest-and-greatest, that now I'm stuck using the radeon driver, which, as is common knowledge, doesn't support any accelerated 3D operations at all. 2D and Xv work fine, though, quite possibly even better than fglrx -_-".
I am actually growing jealous of those people having smooth experiences on their nvidia cards, which is incredibly ironic: I *used* to own an nvidia-based laptop, sold that one, in the time they were getting severe performance regressions, and bought myself a nice high-end system with an HD4870 in it.