Gmail has four new items in its labs section, all of which enhance the links people have included in their messages. You're now able to flip on support for Yelp, Flickr, Picasa Web albums, and YouTube. Doing so will turn a link from one of those sites into a full-quality preview of the content you'd find on that site.
For instance, if someone has included a YouTube link, it simply shows up at the bottom of a message, just as if they had included it as an attachment. (You are less likely to get Rickrolled, that way.) The same goes for Yelp reviews, and individual photos and albums from Picasa and Flickr.
Gmail had previously done this for information embedded within messages, including package-tracking numbers, dates, and addresses, all of which led to a related Google service. However with the addition of Yelp and Flickr, Google is opening this up to third parties.
In fact, the official Gmail blog is encouraging interested parties to submit their own site to be added as a preview, which could lead to a whole new subcategory within Gmail labs.
With this addition, it also brings the tally of Gmail labs add-ons past 40. It may be time for a better way to sift through all that information, especially if the company intends to add more of these site preview options. In a meeting I had with Google back in December, Gmail product manager Todd Jackson had said this was something that was being considered.