Ever wonder what a search engine spider sees when it crawls your website? They may not see what you think they see. For example, search engine spiders typically will not interpret javascript - they only see HTML. If you have lots of content that is only displayed by javascript, the spiders may not be indexing it. So are they crawling links in those fancy DHTML menus that you spent hours creating? That's probably something you should find out!
There are many tools on the Web that will show you what a search engine spider sees. Here is one of the better ones that I have found. Just enter your website or web page address in the form to see what a search engine spider sees when it crawls your website.