Lots of buzz about Google's new Latitude application which allows uses to track friends, family members, lost cell phones, etc... Apple has a similar app for the iPhone, but it is device specific. Latitude will work with any phone that has is data capable (except the iPhone and a few others) and it's free!
After using Latitude for a few days I have few notes...
1. Was the name Google Stalker taken? Latitude does offer some privacy controls, but you have to make a point of taking yourself offline.
2. Make sure you have a data plan (unlimited or lots of bandwidth). To use on a mobile device, you must install Google Maps which actually a really cool little app and it's also free! I have no idea if Latitude works overseas, but the roaming data costs could be a problem.
3. If you don't have a GPS enabled phone, forget about it. The triangulation method, using cell sites, has a radius (for me) of about 5,000 meters which is a little over 3 miles--huge radius for urban environments.
Overall I really like the app. There are lots of privacy concerns, but in the information age that comes with the territory. I tried to do some Googling to see how much location data the cell phone carriers keep and for how long and couldn't find a concise answer. Lots of links on this data being used in criminal cases, so I think it's safe to assume the carriers have the data and keep it for some length of time.
If the carriers have this data, and there is no way to opt out of collection, then the new concerns presented by Google Latitude are minimal.
Google has a record of delivering cool new products, at low or no cost, to get user adoption and then evolving the product over time. So what will the future hold for Latitude? I'm thinking targeted adds, more traffic through Maps, and maybe more online interaction (think chat with proximity).