Recently stumbled on whrrl.com, which is yet another place-based recommender/annotation system that runs on mobile phones. The tagline is "Share real-world adventures and discover places, events, and people through the chronicles of others". Why do I blog this? As lots of similar system (mobile/social software actually), the difficulty lies in bootstrapping the process, or how to have a user-based large enough so that "something happened" out there. For that matter, the FAQ is interesting as it describes to the users how things can be eased:

"But what if I don't have any friends in Whrrl yet?

First off, invite some! Whrrl is all about tapping into your friends' knowledge about the real world and sharing your own with them.

But let's just say for the moment that you don't yet have any friends in Whrrl. Try this: find a couple of places you love. While you are contributing your own reviews for those places, look at others who have reviewed them and share your opinions. Then become a fan of these folks. Suddenly, everything they review is at your fingertips—now you can see interesting places they like displayed right on your map. You'll also be able to filter based on the reviews of people you became a fan of."