>The Hackers Guide has very little (according to the index) and on-line help doesn't give a lot of help on triggers. So either they've been left out on purpose, or their just not very important. Can someone tell me about them? Like, on an update, does the trigger get fired for the current field every field, once or every time? Anything you could tell me would be usefull.

The update trigger gets called when you leave the field. Use the event tracker to determine what is being called when.