To address the concerns of the German public and data protection authorities, Google's just explained in detail what data its Street View fleet gathers as it transits the highways of the World. It's a lot, and more personal than you may expect.
The Street View cars collect three main data streams, and they're pretty much what you'd expect. First up, the vehicles have accurate GPS logging systems to keep track of exactly where they are at any point (feeding into Google Maps' street atlas accuracy). Next, they capture continuous 360-degree imagery of the environs, which is the main data source for the Street View system that can plop users into a pictorial representation of a street locale pretty much anywhere on the planet. To augment this, there's a 3-D scan of the street sides too, which helps Google make accurate representations of building frontages.
But there's a fourth data feed, and it's one that's stirred things up in Germany. The Street View cars are also equipped with powerful Wi-fi antennas that constantly sniff the nearby airwaves as they drive. The attached computers then log any found network's SSID (its name) and the unique MAC address. In other words, if your broadband router is named for something personal or daft, and Google's data fleet has swished by, then Google has a log of your data.
Should you be concerned? Authorities in Germany apparently were but, as Google notes, they're not the first company to collect this data, and with big well-known names like Skyhook and the nation's own Frauenhofer institute already collecting this publicly available information there shouldn't really be any thing to worry about. In particular, the search giant notes that "we cannot identify an individual from the location data Google collects via its Street View cars" other than to perhaps ID your network, if you've renamed your router's SSID to "John Smith's network." Google also only harvests this info to boost its geolocation powers—it's effectively the "A," for "assisted," part in the A-GPS systems that power smartphones. Google's collecting the info for itself to give devices like laptops, which often don't have built-in GPS, limited location-aware powers.
Obviously aware that any data Google collects about its users generates potentially negative PR, Google also explains what of this information it shares to others: Surprisingly little. While triangulated geolocated SSID info may be shared, Google says it never gives your MAC address data to anyone. Of course all it would take would be one legal challenge to really test how far Google goes to protect your information (particularly apt given the PC data seizure shenanigans going on in the Gizmodo/iPhone affair right now), but for Google this is a pretty frank promise to look after you.