First of all, they are extra overhead. Extra overhead does nobody any good. They add complexity to the file system. Extra complexity is bad, all around. Much simpler to have links listed on each page, than to split your page into a bunch of different parts.
But you know, that's okay. Different styles call for different techniques. If they're used correctly, they can be an okay feature. Not one that I would choose to use myself, but nonetheless, nothing I would take offense to. No, the problem is with the authors of these framed webpages. Many of them simply don't do a good job. The mentality seems to be, whoa cool, frames! I want to have frames on my page. Without much of a bother to really think it through.
One of the big problems I have with frames is people who don't target their urls properly. Many cases, when you click on a link on somebody's page that is outside of their site, the page simply opens up inside the original frameset. Now that's damned inconvenient isn't it? Here you are, trying to look at this other site, and your screen area is reduced to a frame. And on the side or top or whatever, you've still got stuff from the old site. Well, I don't know about you, but I don't really want to see that stuff. If I want to go back, I'll press the 'back' button, thank you very much! That's what it's there for! So if a site does that to me, chances of me returning to that one go way down. I mean, if everybody's site were like that, you would have the potential to fill up your screen area with like twenty menubars from twenty different sites! That's totally ridiculous. And there's the total incompetence ones of course who target their entire frameset. Resulting in this infinite recursion scenario that gives you twenty of the same menubars! Even stupider. Luckily, this rarely ever happens. But did you know, that some web authors actually think that this is a good thing. I'm serious, I read an article actually encouraging people to do this. I was astounded, to say the least.
Another problem, is with the url. If you click on a link, and the new page opens up inside the frame, you will still have the original url! Because it is the same frameset, and only the url inside the frame has changed. So you could be at www.yahoo.com or something, and have the url at the top of the page read http://www.geocities.com/brassman327 or something like that. Which is ridiculous again. I want to know where I am when I go somewhere! This applies to in-house sites as well. Once you go to a framed page, the url never changes. You can never tell which file you're working with. As a developer, this can cause major problems, no doubt about it.
Add to this the fact that many browsers in use today cannot support frames, and most of these framed pages don't have graceful degradation -- something like 8 or 10 percent of people won't be able to view your site. What else? Oh, what about these people who make their frames fixed? It forces you to keep your window at a certain size in order to be able to view everything.....and I hate to be forced into anything! It forces the author's view of his pages onto the reader. And again, I don't like to be forced!
Ah well, I guess that's enough ranting for now. Again, some people use frames properly. And while I still don't like it (you'll notice that my site is blissfully frame free), it's those people who don't bother doing a proper job of them who really piss me off.