Active Directory login takes from seconds to minutes on OSX Login screen loads a very long time occasionally. It's annoying to wait for 5 minutes just to be able to use the MacBook. I have not been able to find a reason why it sometimes takes a very long time and sometimes loads instantly.

I have a MacBook Pro with in OSX 10.6.6 and Active Directory corporate Windows network  controlled username and password. I also use a setting that requires password login after 15 minutes of sleep or screensaver in case I forget my laptop on a train or something.

What can be done to solve this issue?
There are several ways to get a Mac to work on an Active Directory network. Apple has some issues with it's Samba implementation that seem to cause these sorts of issues. I have been using software from Likewise to join our Macs to our domain. Starting with version 6.1 (currently in pre-release) the issues that you describe are greatly reduced (not eliminated) -- it still takes me about 45 seconds to log in.

If you have administrative control over your Mac, then you will certainly want to read up on migrating from your current AD implementation to Likewise. If you are not a admin, then you will need to speak to your IT department. It is important to note that Likewise should be installed as a local admin, and upgrades should not be applied as a domain user (even if they are an admin), but as a local user.