File this one in the "new to me" bucket. I went to check into Sloe in Paddington Station on Foursquare on my HTC Desire - and was told that Paddington itself was trending.
What does this mean? Aside from making flashmobs and swarm badges easier it will help surface popular venues to Foursquare users.
For example, bigmouthmedia took a stand to Internet World (London) this year. I noticed people checking into "Internet World" and (perhaps more correctly) Earl's Court 2. A marketing idea would have been to get the bigmouthmedia crew and visitors to check into a sub-venue, our stand number, as that would likely encourage more visitors (the social savvy sort of visitors I like too).
SMX London is up in a few weeks. I should very much hope we get the 50 or so check ins required there for us to unlock the swarm badge. If not we should certainly get a trending topic.