[larrik]

I think Mongo is GREAT at one very important thing:

Storing other people's data.

If you need to consume other services, especially if its more than one, it's hard to beat Mongo (or other NoSQL databases). You get a lot of search power (not always the easiest to tap, but you get it), and your app won't break when they change their formats. If you need a LOT of it, even better.

I would never use it as my main datastore, though. At least not for any projects I can think of offhand.