I've had a spin around Plazes - a European based social networking site. The basic idea is for people to share places they like. Simple enough. Some nice features makes for a good foundation. However, the BETA product has some critical limitations.
For once, it's not clear why "I have to use this." I mean, there's a lot of sites out there, such as Yelp, that gives me useful information on interesting places, cafes, bars, car-repair shops. What's is the unique value in Plazes? It's possible that there is something truly unique in the combination of features, but the value is not clear upon entry and that could turn off many prospective users.