Check if Network Accounts are avalible
A quick check that I will use is the id username command in terminal, replacing username with a user other than the one you are logged in with.  For example, if I'm logged in as SJobs I would instead use the query id TCook, assuming that TCook is another user within the domain but not on this computer.  This will attempt to query the domain for the specified username and return all of it's values.  If you are not currently connected to the domain it will instead return "no such user".

If this fails I go back, check my binding, check my network connection, log out and login again.

Hope that helps!