Intel's driver has worked with DRI2 already, but now it's finally entering their mainline tree to appear in Intel's next driver release (xf86-video-intel 2.6). This support isn't yet perfect (DRI2 vBlank-synced swaps are still lacking), but it's a sign that the Intel DRI2 implementation is now ready for adoption. DRI2 was dropped from X.Org 7.4 but will appear in X Server 1.6 after its October revision. ATI support for DRI2 can be found in an experimental driver.
Kernel-based mode-setting support has been planned to enter the Linux 2.6.29 kernel and the Intel support for it appearing in drm-intel-next (Intel's staging area for code that soon will go mainline) confirms this will take place. To use KMS, you'll also need to use the GEM mode-setting branch of libdrm.
Additional commentary on these two events can be found on Eric Anholt's blog.