Who the heck are these people? Highlight's social overload

South by Southwest hasn't even started yet and already the friend-finder app Highlight

is being pegged as one of the most important new mobile apps of the show. It's a little app that alerts you when friends, and friends of friends, are in the same place as you at the same time.

Unlike Foursquare or Facebook, it works without requiring check-in, which is what makes it cool. The serendipity factor is just through the roof. It'll tell you if a person you know (that is, a Facebook friend) is in the coffee shop where you are standing in line. That's assuming they are also a Highlight user. Which, if they're a geek in the Bay Area or at SXSW, is pretty safe bet. This thing is taking off.

As Robert Scoble says, you can tell this app is important, because it's already winning a bunch of haters. And for good reasons. In fact, I have two.

I've been using the app for barely 48 hours here in San Francisco, and already I'm overwhelmed with alerts from it, because Highlight seems to be designed to help you connect with people you don't know just yet: your Facebook friends of friends.

That's a lot of people. Too many, in fact. Now, Highlight is new, and it does have enough information to do a better job of filtering the people it tells you about. Already it shows you how much you have in common, according to Facebook. But it needs to layer in some filters that use that data, or it's quickly going to get overwhelming. Especially at a mob scene like SXSW.

Then there's the creep factor. Highlight shows you, on a map, where a friend or FOF is, if you are close to them at the same time. And then it remembers those intersections for your later perusal. Pretty cool if you're sitting down at a work lunch, driving down Sand Hill Road, or at a conference. Not so cool if you're chilling at your house. Someone you may not know walks by, and they get your location pinging them on their phone. That's just creepy.

Both of these are solvable problems. Problem one can be solved with filtering. Problem two can be solved with geo-fencing: the option to not tell people where you are when you're someplace you want to withhold from the app.

Variable privacy in location apps is complicated and will confuse users, but a passive location reporting service like Highlight really needs it. This app is skating on thin ice right now, ice that Path, for one, has already scored near to breaking.

Users' location data is incredibly sensitive. Being a hip startup doesn't excuse a company from being cavalier with it. Highlight needs to grow up. A lot.

And I hope it does, because it is one of the best examples in a really interesting new category of app. See also: Glancee, Kismet, Nixter, Buddha, etc.