When it comes to value-added software on Android phones, I'm typically first in line to call "gimmick!" But today, Sony announced a new service for Xperia phones that actually sounds genuinely useful - my Xperia. It's pretty simple, really. You get a web UI that allows you to track your phone on a map, cause it to emit a sound (it even overrides silent mode), lock it and display a message, or remotely wipe it. And when it comes down to the necessities, those really are the four you need for a "find my phone" solution.
Oh yeah - Google account integration.
The pilot launch is extremely limited for now: only Xperia Acro S devices in Nordic countries are supported at the moment. However, the trial will expand to other Xperia phone models shortly, and eventually to other regions. If you own an Acro S and are in a Nordic country (or have flashed Nordic firmware), Sony will selectively send you a notification to participate. If not, you'll just have to wait.
There's no indication as to whether or not the service will be free once it gets out of the pilot stage, or at what point the trial will end. You can find out a bit more at the Sony Mobile Blog, where there's an 'interview' of sorts with one of the software's creators.