For those of us using Blender 2.5x the problem with rigged mesh not exporting correctly is a known issue. A couple of days ago Tapple Gao posted a fix for that problem in the SL Forum. See: Rigging working in Blender 2.5
This is a geeks only fix. The fix submitted to Blender.org is code that must be used when COMPILING a version of Blender. The fix is simple enough, simple as in short, and I suspect will be in the next release of Blender.
Someone may put up a build of Blender with the patch implemented. Until then the fix doesn’t do most of us any good.