Frames were usefull before the masterpages feature was available on asp.net 2.0, but I recall the problems I had with frames was that it tends to mess up when trying to bookmark a certain page, web search engines tend to link to pages outside of the frame context (so the frame doesn't even load when going to the page), printing a page from a site that also had frames was a pain, and also sometimes if your page is too long or out of size with the frames, it'll cause those annoying scrollbars to appear so you have to make sure everything is always adjusted correctly.