Scott Mitchell over at 4 guys from Rolla has just posted a great article on solving multiple submit button issues (http://aspnet.4guysfromrolla.com/articles/010908-1.aspx). Basically he talks about issues when you have more than one button on a form and a user presses enter (the first button on the page is pressed instead of a the button relating to the controls been filled in).
He didn't cover one technique I normally use however which is to use a panels default button attribute. This specifies the button which will be clicked when enter is pressed when a child component is highlighted.
Nice article though, and well worth a read.