When I started using "Project GC" (through a hint of another cacher), I first found the "compare maps" the most useful feature, because planning common tours with other cacher colleagues is made easy. At the end of the current year I liked to use the "de-GAP-ing" my 366-matrix, which worked through generating such calendar entries (appointments "Find a cache today"). Currently I'm surprised and much pleased with lots of challenge checkers and their capabilities and the possibility to extend them with new markers for new tasks. I also until now used only one time caches along a route with the very good filter capabilities in combination with the virtual GPS, which is very helpful for planning.
Overall and over the time I'm satisfied with the stats generating in background and easy binding to GC profile, the very fast reactions by ganja (seeing in the forum here and on the site at all), which took me (initiated through a merchandise action some months ago) to the decision of paying this service and trying to convince more cachers of this great service. All the time a found more and more usable features and I guess, I'll find more the next time....