I saw recently on the Google blog that the Googlebot will start submitting web forms.

Specifically, when we encounter a <FORM> element on a high-quality site, we might choose to do a small number of queries using the form. For text boxes, our computers automatically choose words from the site that has the form; for select menus, check boxes, and radio buttons on the form, we choose from among the values of the HTML.

They also listed some important limitations, which makes this seam much less extreme as it did when I first read about it.

The Googlebot will NOT submit forms that:

• Use method="post"
• Have password fields
• "Use terms commonly associated with personal information such as logins, userids, contacts, etc"
• Have a form action that is forbidden in robots.txt