I have a lot of respect and admiration for the lengths that ATI goes to to release information to the public.  Last year they made the Radeon 6xx series ISA available.  In the last couple of weeks they've released details on 3D registers in the 6xx/7xx series, and the (albeit primitive but not simple) r600_demo (via git from freedesktop.org).  The availability of this kind of information is a huge boon to hobbyists, researchers, developers, and pretty much everyone else that cares.

I've given all the above resources a look through and I hope to spend a bit more time pouring over the r600_demo (not for the faint of heart or API-dependent).  Thus far I've only had access to documents related to NVidia hardware from the previous generation (under NDA).  The differences are seemingly non-trivial but I'm not certain if it's a result of genealogical advances or manufacturer architectural differences.