Top Locate, an Irish security firm based here in Dublin, have launched a new service for locating a person via their mobile phone (where GPS is supported), as well as providing a panic button style service which can be activated by the user if they feel in danger.
It is an interesting product but I am not sure if I would buy one. Perhaps it would make the middle classes feel more secure allowing their children walk to school, but then again that's why they have SUVs ;-)
Top Locate : http://www.toplocate.ie/
Updated 2021 : note that the above post is out-of-date, given this post was originally published in 2007, but is left here for archival purposes. I have unlinked the original external link as it is now dead.