It depends on how well you've set up your pages. If you have a lot of other stuff on your pages competing for visitors attention (like on the five column homebizseo site in your signature) you should only expect a low CTR. I truly believe that anyone who isn't getting at least a 10% CTR simply isn't trying hard enough. But I can see why some don't get that much. Often their site layout/design doesn't do a good job of putting ads in visitors faces and because changing it on hundreds of pages can be a major job many people just don't bother with it and end up with sub 10% CTR's from here to kingdom come. Of course, there are probably some types of sites that will never be able to get over 1-2% CTR no matter how good the layout of the pages is. For example, in the majority of cases it would probably be quite difficult to tweak, say, a forum sufficiently enough to maintain a high CTR. So, ultimately it comes down to both the type of site and the layout of it.
What would be bad about a CTR more than 10% -- unless the clicks were fraudulent. Of course, a CTR of 1% is bad if the clicks are fraud. It's fairly common for pages with good content, high ad relevancy, good ad placement, and good ad blending, to achieve 70% CTR -- with legitimate clicks. Nothing wrong with that. It would be rare to have an entire site's average CTR to be that high, but 10% or so is not uncommon.