boost::lock_guard vs boost::mutex::scoped_lock

Which is preferred boost::lock_guard or boost::mutex::scoped_lock?

I'm using Boost.Thread with the hope to move to C++11 threading when it becomes available.

Is scoped_lock part of the next c++ standard?

Are the any advantages to prefer one over the other?

NOTE: I'm aware that scoped_lock is just a typedef of lock_guard.

edit: I was wrong scoped_lock is not a typedef of lock_guard. It's a typedef of unique_lock.