Gmail has released a few Gmail Labs features that show useful information related to your messages. Gmail's gadgets detect links to YouTube videos, Flickr photos, Google Docs documents or Yelp reviews and show previews below the email. The gadget that lets you preview YouTube videos is now a standard Gmail feature, while the other gadgets can be enabled in Gmail Labs.
Wouldn't be nice to develop similar gadgets for previewing content from other sites, for showing public information about the sender or for performing repetitive tasks directly from Gmail? Google Apps started to offer an API for contextual Gmail gadgets, but it's only available for trusted testers.
"These gadgets can smartly draw information from the web and let users perform relevant actions based on the content of an email message, all without leaving the Gmail inbox."
Google says that these gadgets "can boost employee productivity by complementing email in a context-specific and actionable way", but I'm sure that they're a great way to extend Gmail for all users. For example, a cool gadget for Blogger users could let you moderate comments without opening a new page or reply to comment directly from Gmail.