[SL avatar mesh bone deform in blender]

You can make them longer by translating(moving) the bones before you skin the mesh, using scale on rigged bones generally doesn't work in most systems.  If your still getting issues after upload you'll need to adjust it with the avatar shape.  To correct your posing issues you need to make an animation that will rotate the bones into the correct positions, quad avs look terribly silly without it.

[3ds Max - Exploding Mesh Issues]

When you import your av into SLAV what scale are you using?

[MAYA: Multiple Textures on 1 mesh]

It does not work if your exporting from Maya 2012, you have to export it as an FBX file using the 2011 profile then use the Autodesk FBX converter(free download) to export that as a DAE file.

[Problems uploading meshes]

One more thing to check, is your root bone named Hips or mPelvis? I found when moving back and forth between animating and rigging that if I left the root bone name Hips it would cause similar results.