I've been speaking with a number of people who had this problem (and I did as well).  The gist of it is, when you try to use the built-in documentation browser in the Xcode organizer, you are prompted to enter your password.  (Which you can't actually do)

The solution was non-obvious to me, but here it is:

1. Open Preferences > Downloads
2. Choose the Documentation Tab
3. Click "Install" for the documentation sets you wish to use

Once they're done installing, you'll be able to access the docs normally.