GPS Tagging seems to be the next big buzzword in this all_to_do_well web2.0 hype. GPS Tagging essentially means attaching geographical information (long,lat,alt,etc) to a given media type, for instance images, and then mapping that media. Flickr and others have done this rather successfully and it is really hitting home.
I have done something similar with this interactive map. I have added the capability to add images, links, comments, and soon to add a few more bells and whistles. I also have the ability to overlay topographical maps for a given area. There is geographical data for nearly every body of water (with some exceptions) in the United States. With that said, it is possible, given a specific region (due to the size of the database), to create an incredibly interactive mapping system. A few drawbacks from the current Google Maps implementation is that the map resolution hasn't caught up in less populated areas. I now have the data from the HotSpots page deliverable in KML format, which is what Google Earth uses to define locations. Google Earth is probably about the coolest free geo utility I've seen. It does some amazing things and there is a terrific community of developers coming up with new ideas.
What I would really like to do next is focus on a particular region as sort of a test subject by pooling together (pardon the pun) the lake/river/etc data and combining it with user input. Aside from catching fish whilst perusing the site, the possibilities are near endless. The ability exists to keep certain data private from normal access which means that a group of individuals could create their own private map system. Does this sound like fun or what?
I'm running a poll at http:/www.shawngo.com/hotspots.php and was curious if anyone had any more input of what they think would make this application really useful.