Mesa 7.1 is a development release in the work towards Mesa 7.2, but most Linux distributions will adopt this release and it should prove to be relatively stable. What makes this release very important though is that its been holding back the X.Org 7.4 / X Server 1.5 release. Mesa 7.1 is a prerequisite for building X.Org 7.4, but now that this 3D library is out the door we will hopefully see the X.Org update very soon. Ideally this means a release this week or next week (perhaps before XDS 2008). X.Org 7.4 was supposed to be released in February of this year and then May, but it's been long-delayed.
The Mesa 7.1 release announcement can be found on the mailing list and the source files can be found at SourceForge.