From my personal experiance with my Intel Pentium-D with GMA 950 I can tell you that the MESA folks are making very good progress.
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I think that once the memory management stuff gets sorted out with Mesa then you will have decent engough performance out of the x3000 for most Linux games, maybe even including Doom3 (with all the details turned down). (although I realy doubt that you'd be able to get away with playing online with Quake4)
I am hoping that they'd should have the memory management stuff stable by 7.3 release, especially this this would increase the usability (reduce memory usage, for example) of things like Beryl or Compiz to the point were it can be used by normal people with no sweat.