GMail apps

I was just ordering some books sent to me as requests by faculty in over email. Wouldn't it be cool if we could write our own apps that would live inside GMail and could operate on the information that came through in email messages? In the same way that Google Calendar recognizes dates and times in email messages, an application could recognize book titles, ISBNs and do some checking on our catalogs, and eventually help place an order for the title if desired.

Since GMail is web-based, I suppose you could use any kind of browser embedded application like Zotero or LibX to take these kinds of actions, too.