"Hotlist" does not ring a bell, but yes, that seems to be like my idea, although Hotlist appears to be limited to Facebook and Twitter, because: "So you want to go out but aren't sure which place has the crowd or event you're looking for? Hotlist enables you to take a peek inside of venues to see the crowds before you head out. Read reviews and real-time Tweets, discover upcoming events, and check out key stats like the guy-to-girl ratio and the general age of the crowd, all from your computer or smartphone. Then use Hotlist to coordinate with your friends on Facebook." (#1)

I'm reading through the articles on their Wikipedia page (#2), to better understand what they do, and how it compares to my idea. Thank you!

#1: http://hotlist.com/about

#2: http://en.wikipedia.org/wiki/Hotlist