I completely disagree that the singular is worth more than the plural. "Locals" are people who are from a specific area. There is also a brand of sandals called "Locals" and there was a move called "Locals," albeit, the real value of the name lies in the first meaning. I think this would be a great name for a dating or networking site. Instead of having to brand something like LocalSingles.com, LocalMen.com or LocalWomen.com to get across what it is, Locals.com encompasses all of it without having to use a second descriptive word.
A second thought is that the name could be a great travel information site. When I was in Jamaica in January, I didn't want to ask the concierge where I could go for some good jerk chicken, I asked some locals instead. I've always found better places by asking the locals.