Like all tools, FB is only valuable if you learn how to use it.

The private messaging is indeed private and the filtering capability for deciding who gets to see what can be managed down to the level of each 'friend' and works perfectly.

If you find that one of your 'friends' has a tendency to post updates which are of no interest, you can hide either the post in question or all posts from said 'friend'.

It's like all of these things. Read the help pages. Read the forums. If you're going to use it, then learn how to make the best of it.

one tip for free.
A good place to start is to organise your 'friends' into lists (close family/colleagues/bandmates/ex-wives/people I've only met once/....). This makes it easier to customise distribution of your posts.