Google is experimenting with emails being included in personal search results. This means that when you search for something in Google, relevant messages in your Gmail will show up in the right sidebar. You can sign up now to get early access to this feature.
Searching both your emails and the web may be more convenient than separately searching Google for regular web results and searching Gmail only for emails. Google is also adding an enhanced flight-tracking feature that shows details for upcoming flights pulled from your emails when you search the web.
Right now, this is just a field trial, so the unified search may not actually be implemented. You can join the trial via the link below so long as you're not a Google Apps user. It's a limited trial, so get clicking if this sounds like a useful feature to you.