Just read the blog from Matt Cutts entitled "Solved: another common site review problem", that Google is working on (experimenting with) following form links now, meaning GoogleBot will submit some queries from a form and see where it is taken and crawl those pages.
More information is availble at the Google Webmaster blog: Crawling through HTML forms
Now, it is still on experimental basis. Mr. Cutts says only a few select sites are currently being tested, but for SEO people and especially us programmers who try to keep up with the progress just a bit, this opens up a whole new ball park if indeed the feature gets implemented on a more permanent basis.
I suggest reading the sources to see why Google is working down this avenue, because it also shows why it is beneficial for us programmers.
Interesting in my own personal little opinion, and it is a path which will make life a little less confusing for us programmers when we try to solve problems for our clients.