To expand a bit on Chris and Robin's posts, nearly the entire development team is currently focused on fixing them. 1.6.5 should give us significant head room, but that is not the only planned change. Login and related scaling issues will remain our primary focus until we are certain that we can scale SL to many times the current user base.
I know that the current problems are incredibly frustrating, so please help us by testing out the 1.6.5 preview. In addition, expect a pretty rapid sequence of previews and releases over the next weeks and months in order to put these problems to rest once and for all.