I have noticed that dynamically-user-generated pages, like search result pages (e.g. mydomain.com/?search=chocolate+sardines), often get crawled by GOOGLE shortly afterwards, which is kind of spooky - I always guessed it was due to having Google code like Adsense, Analytics or FeedBurner on my page, and I quite like that anyway - free content! But how does YAHOO do it?! I don't have any Yahoo code on my pages, yet I often get Yahoo crawling such dynamically-generated pages, even though they never make it into my sitemap and I can't see where they would get the link from. Maybe they are sharing data with someone else?
Adsense, Analytics etc. doesn't share the data with google search. Google, Yahoo or any other search engine crawls your sites and get the information from the links on your site itself. Sitemap etc. are secondary and not given too much importance. If you are linking to a dynamic page, SE will not have any problem picking it up. It doesnt submit the form to search though!
But this is it - I am not submitting these links to anyone, there is no way for Yahoo crawl to find them. A user visits my site, does a search, and a few days/hours/minutes later I get a visit from the Yahoo bot to that exact page. Google does this even more often, sometimes I get a Googlebot hit to that page within seconds - I know, I tried it as an experiment!