There's MobileMe for iPhone, My Phone for WM/WP7, I'm heard of various apps for Android and I'm sure there's something for BlackBerry. But what are these like in practice, specifically for finding and if necessary wiping a lost or stolen phone? People seem to say the (admittedly expensive) iOS MobileMe is quite reliable, but has anyone had first hand experience of any of these tools?

The only one I have personal experience of is My Phone for WM6, and frankly I'm not impressed. It only detects location some of the time, and only then during a scheduled synchronisation. I regularly find it reporting last known location as where it was a week or more ago. And I can't get the "premium features " (including remote wipe) to work at all, even though my phone and carrier is supposed to be supported. The only good thing is the price (free for location only).