One of the many things I really enjoy about this website, is this q&a. Before I found it, there were questions that I couldn't find the answer to, now I can get answers from a range of different views, and people get rewarded for helping me.
I also like the Badge-Gen, which motivates you to go caching and achieve new badges. I like how there is a variety of Badges to achieve that will suit different geocachers.
Another cool feature is the Finders of my caches, in which I see who regularly finds my geocaches.
Project GC is still my favourite Geocaching resource.