The current stable release of Blender remains 2.49b. In Second Life two of the main sculpty tools use Blender: Primstar and JASS2. Both of those still use Blender 2.49b. However, the beta versions of Blender 2.5 are becoming popular with those working with mesh in Second Life. The reason for that is the Collada Export/Import features in Blender 2.56a have more fixes. The Collada features have just been updated again and this week more work will be done on Collada.
To Get 2.49b or Not
Even if you have never used Blender, you have likely heard it is difficult to learn. Unfortunately that is true. However, the new 2.5 versions are much easier to learn, or at least it seems that way. The 2.4 version are still very much keyboard shortcut oriented. One mostly has to memorize those shortcuts and they are anything but intuitive plus there are so many. The new 2.5 version are much more menu complete and the menus are better organized, though some may argue that point.
So, if you have skipped learning Blender because of the difficult learning curve, you may want to reconsider. If you are using Blender 2.49b for sculpty creation, you may want to wait until the new version of Primstar and JASS2 support 2.5. However, if you are building mesh for SL then Blender 2.5 is probably your best choice. Just know that using 2.5 puts you on the bleeding edge.