Kudos to AMD for releasing their new graphics cards, and for being able to release them at great bang-for-buck prices!
I have a G92 8800 GTS right now, and am contemplating an upgrade to a 4870, both to improve Windows game performance and to show support for AMD for their open-sourcing efforts. Though I game in Windows, when I'm not gaming I'm almost exclusively in Linux, and prefer to use open-source whenever possible.
So my questions are: Does radeonhd and/or radeon support the 4870 yet? Do they support 2D acceleration and enough 3D to run compiz-fusion? If not yet, when will they be able to?
xf86-video-ati should work with the Radeon HD 4870, albeit without 2D or 3D acceleration at this time. However, the xf86-video-radeonhd currently has no Radeon HD 4870 support. The -ati driver should work due to its use of AtomBIOS. I have that open-source driver running great with a Radeon HD 4850. There should be open 2D/3D support in a few months...
For now, however, the Catalyst "fglrx" driver does work with the Radeon HD 4870.