The other sites are "social." (Which is different from social; nobody out on the ride with you to talk to, trade off in the front of a paceline, etc.)

The unit itself is pretty awesome. Best feature on Garmin Connect is the calendar, I think. I upload the interesting stuff I do, and I can look back at when I did certain rides I want to repeat and get an idea when things will be melted out enough. Plus it's good motivation if you need that.