Dave Hildebrand.com

For anyone who uses Microsoft's Windows Server Update Services (WSUS) and needs to force a client to check for updates, you can run the following command and the client will check with your WSUS server.

wuauclt /detectnow

This method is much faster, it usually takes only a few minutes, compared to the old way of deleting keys in the registry (& much safer too).

A good resource for admins running WSUS is at WSUS Forums.  The folks there have helped many WSUS admins through many errors and mis-configurations.