I was surprised to find that the Adsense custom search thing that's a part of Google Adsense doesn't actually index all the content on my site!
The site is about 10 years old with several thousand flat .shtml files on it (no weird auto generated files or anything like that). I've been using the Adsense search thing for several years.
Given that *lots* of people (like me) use custom search as the primary (if not only) way for punters to search the site, doesn't this mean that it's not really a very good choice as one's primary search method:-P
Kind of crap really, isn't it?
Then again, if punters can't find the "hidden" content on my site I suppose they are more likely to click on an adsense ad on the search results page, so at leat I get some money out of it. Funny old world, eh? Maybe Google should not bother indexing ANY files then punters would have to click on the ads 100% of the time!