That got your attention - the biggest usability problem in my opinion is the horrible single form you're usually forced to deal with - I know
Paul Wilson has a
multiple form control for sale, and it is really cool but there is an easier way for most people. To see an example of what I mean, have a look at the
ASP.NET site, enter a search term then hit 'enter' - nothing happens! Now, this is only a pain because its' not the expected behaviour - see
Steve Krugs' excellent book on web usability,
Don't Make Me Think for more on this type of issue... There is a solution however,
Andy Smith - all round server control genius - has a
DefaultButtons control which simple lets you specify which button is clicked when you press enter in a textbox... You'll be surprised just how much difference this simple improvement to your ASP.NET sites can make to user experience.