Some Transformers don't seem to be registering that an update is available and I haven't seen a reasonable explaination for it yet. That being said, the 3.1 update is on the Asus website (the link is in Phil's Transformer sticky:
http://forums.androidcentral.com/as...sformer-manual-usb-drivers-sync-software.html) - thanks, Phil. Just download and manually install (instructions for that are in the thread "I just got my Asus EeePad Transformer and I have a few words." on page 6 or thereabouts - #s 55 & 57). If you have the dock, make sure it is attached and it should then notify you of a dock update - if applicable).