I see a lot of you guys use Strava - are there any particular perks to this as opposed to other GPS tracking fitness sites? Other stats provided that you have to pay for on other sites?
The only other site I've tried myself was Garmin's own (Garmin Connect). I like Strava better for a lot of reasons, including the leaderboard system since I have a competitive streak, the ease of looking up old rides and performances on particular climbs/etc, and I find some of the pay-for features useful too.
For an example, maybe I go for an after-work training ride and tackle the local time-trial course with my studded-tire mountain bike in the winter. I can see "ok, I finished it in 35m 30s today," pull up Strava's Leaderboard for the TT course, then choose "My results" and see that it's my 5th-best performance overall.
But I want to compare just the times I was on studded tires, they make the bike much slower. Since the bike is listed separately in my Gear in its winter configuration, I can eyeball the dates of my better performances. 4th-best was in February? Undoubtedly on studs, let's check... yes.
So in this hypothetical example, I learn that I'm about 45 seconds off my PR with that equipment. MUST. TRAIN.
edit: oh, and another thing I find handy is the Compare function, where I can compare any one of my performances to my own PR and the course record-holder's performance. As I move my mouse across the graph, dots on the map and the graph show our relative positions on the course, along with a readout of my speed, cadence, power and heart rate at that point on the course.
That kind of drill-down granularity is way beyond anything a guy can do on Garmin Connect. Also, many of our local athletes are using Strava, so it's sort of "the place to be" if you want to compete by GPS

Bonus: everything described above is available on the free Strava service.
I also find Strava useful for route research. I can use the Explore feature to look for segments in our area, then use the Leaderboards for those segments to view peoples' full rides and learn where to find the trailhead for an off-road area, for example.