I hope to make simple meshes for Second Life. I think the export in done in collada or DAE. SL reassigns rotation and position when you import. However the scale might need some consideration. SL uses a right handed coordinate system. Eventually I would like to make rigged avatars for SL and I think there is a Blender addon to assist with that. (Avastar maybe)
Eventually if ever I was good enough exporting to the Blender market would be the goal. As the intention of this market is to create content for other Blender users there should be no issues with export but I will have to check.