How to display user info on each view ?

i would suggest to add a before_filter to the application controller,
and get the user object there, from the user id stored in the session.

then in your layout you can always access the user object, and e.g.
render a partial that is showing the user info stuff in all layouts.

Storing the whole user object is not a good idea if your app is going
to have many users, and your users will have a bigger number of columns
than just the basic name-pass-id-created_at etc ... that will just make
the session data too big...