Loopt
Loopt shows you a map, and your position on it, and also the positions of your mobile friends who are in the vicinity. Now you need something to do--somewhere to get together. Loopt detects businesses in the area and makes suggestions based on your interests or specific queries ("beer, pizza, bowling"). You can read what any of your friends have said about prospective meeting places, or read reviews from Yelp to help you decide.
When you've found an agreeable destination, you can then invite your friends, and access directions for getting there, as can your friends. You can also search out new friends by looking for other Loopt users who have similar interests (favorite bars, say) to yours. (http://www.loopt.com/)
Blip.fm
If you think of a song you want to blip, you just search for it (you can find almost anything), make your selection from the search results, write a little comment about it, hit send, and then your blip is added to the stream of other blips. The site then shows you the other members who have also blipped that artist. It's surprisingly engaging and fun, especially if you find good DJs to follow, or if your own real-world friends sign up and participate. (http://www.blip.fm/)
Power.com
There aren't many sites with 5 million users that we haven't heard of, but Power.com is just that, and it's a name you might be hearing a lot more of this year. The "social inter-networking" site, as the company calls it, operates on the premise that many of us now belong to several social networking sites and that it's a hassle to log into and post to each one separately.
Power.com lets you log in once, then view (and post to) any of a long list of social networking sites that you sync the service up with--all from one place. You can see the posts, status changes, and so on, of your friends on multiple social networks, and simultaneously send new messages or updates to all of those sites (similar to Ping.fm). You can also automatically log into, and instant message using MSN from within Power.com--cool.
Actually, Power.com worked a little too well for Facebook's comfort. In late 2008 Facebook started complaining about Power's ability to store Facebook users' passwords and access Facebook users' content. After all, Facebook has its own scheme for connecting to multiple networks at once, called Facebook Connect. Facebook eventually filed suit when talks with Power.com failed to yield an agreement. Power.com says the two companies are now working out their differences. It's likely that Power will still support Facebook, but will have to use Facebook Connect to connect. Without a workable agreement with Facebook, Power.com's utility would be seriously limited. (http://www.power.com/)