Plazes crossed my radar several months ago, likely because of a mention on Joi Ito’s blog. I visited, registered, but never really got what it was for or about, and never returned.

Today I was cured of this through a presentation by its founders Stefan Kellner and Felix Petersen, two super-smart guys from Germany.

Here’s the thing you need to get: location based services — stuff on the web that is tailored, automagically, to wherever you happen to be at a given moment — are hard because, at least right now, the folks with the best geolocating abilities are the mobile phone companies, and they’re not giving the information up, at least not in any sort of open, hackable way.

Stefan and Felix’s brilliant innovation was realizing that they could built geolocation on top of the unique MAC addresses that most every Ethernet router, wired and wireless, have. They have a little app, called the launcher that figures out the MAC address of wherever you happen to be and sends it up to their server.

For example, here’s the Plazes page for the reboot hall. Because I ran the launcher when I opened up my laptop, the Plazes server has the MAC address I’m using, and knows, from other users at the same location who’ve been ahead and “blazed the trail” with information about the location, where I am.

This is such an elegant solution to an otherwise cumbersome problem, that I was smiling throughout their talk. Neato.