I have a fancy, graphically intensive design to convert to HTML. Its navigation has awful (non-standard ofcourse) fonts. I don't like text-replacements techniques that much.
So I'm wondering if image maps would be good for navigation? Are they good or bad for SEO?
If you forget the alternative text on images, the site will be not-navigable for those people using text browsers, screen readers etc.
Search engines will of course find and follow any link they can find on a page. But it won't be easy for people, especially, if you're using SEO-unfriendly URLs with lots of parameters, so that you will never know what is there until you follow the link.
Also keep in mind that some people on dial-up connection (there are much more of those than you think) have a habit of switching off displaying images on pages (to save on traffic since they pay per megabyte). It's the same group who actively block ads in form of banners and especially Flash for the same purpose. Your images-only navigation may piss them off as well.
Image maps can be a good choice for navigation in certain circumstances, as mentioned the alternative text is important for users and search engines. Image maps will likely have an effect on your sites SEO even with alternative text, especially if you are using server side maps (which are for obvious reasons harder to parse), one commonly recommended way to avoid this problem is to provide normal text links on your page as well small an unobtrusive to your design purely for the purpose of the engine to read. I'm sure you have seen many pages using image based menus or image map based menus supply a list of the menu links in small text at the bottom to make it easier for engines and in some cases to increase accessibility.
I always like to think about the html document as an unstyled document first and then lay our the semanitical tags for each section. For navigations I always end up using an <ul> where each menuitem is an <li> with an anchor inside.
This method is far superior to an image map what concerns accessibility and usability. You can very easily create an image sprite of the whole menu and use css to position it in the background.
Check this article for an example: http://stylemeltdown.com/2007/10/22/image-sprite-navigation-with-css/