Meetup is a really solid service. I've used it for many years now, and increasingly so. The activities/in-person focus makes it a much stronger and stickier social network than most.

Also, there's a critical-mass issue that explains why it's built up gradually. Lots of Meetup groups are purely "hookups" or "networking," but the really good ones tend to exist as long tail niches.

Meetup is on the very short list of services used regularly by an elderly friend who got her first computer (an iPad) less than 2 years ago.