There are several companies now with interesting twists on saving and using location data. From the Where 2.0 conference two weeks ago, I covered a few of them. Shortly afterward, I talked to the founders of Flagr, another location tagging site.
Currently, the site is oriented around tagging locations (for example, "pizza") and making it easy to find the tags. The next release, which will hopefully hit the main site soon, will enable users to create private or shared maps, which is a much more sensible navigation scheme for location data. For example, a user could create a map of good pizza places in San Francisco. Other people could contribute to it, making the map a hub of group commentary. Users will also be able to create private maps for collecting their own resarch (for example, apartments they've looked at).
Locations can be entered from a mobile phone. Unfortunately, the GPS capability that some phones have can't be accessed by Flagr, so users have to enter location data. For a place you want to add, you enter a name and a description, and to put it on the map, you either type in an address or just enter the zip code. If you just put in the zip code, the system will do its best to look up the business, find it in your area, and flag the right address automatically. You can easily send pictures through, as well. One big downside: although Flagr lets you upload locations and pictures from a mobile phone, there's still no good mobile interface for reading data.
Of course, you can also tag locations from your computer's browser, and the next version of the Wi-Fi location finder Loki will enable you to automatically bookmark the current location of your laptop.
Also coming soon: more visualizations to help you show where you've been and what you've tagged, and an easy way to export your maps to MySpace. The idea, according to cofounder David Wurtz, is to "give people a way to brag about where they've been." One can also think of it as Digg for the physical world--all Flagr needs is a rating system, and the team is considering adding one.
At the moment, Platial has a more developed group mapping system. Flagr has a strong group-focused design, though, and a lot of potential for growth.