Yup, I downloaded this app a couple weeks ago and I LOVE IT! It's so easy to use. I've showed it to friends and family and they all love it too.
I haven't used the friends feature, but I have recorded a number of work outs (walking, mountain biking and rollerblading) and the GPS has been spot on every time. I enjoy the calories burned feature, which also seems fairly accurate. For 10-15 minutes of intense rollerblading, I burn about 100 calories, which seems about right (also, you can set your weight in the settings which probably makes this # more accurate).
I also like the fact that you can look over your history of workouts and see the GPS map for each one. I'm not using the facebook/twitter results feature, mostly because I don't want my friends to know what I'm doing and when, but I find this app incredibly easy and motivating regardless.
For people who don't have it, I'd also mention that is has almost every workout imaginable preprogrammed. Yoga, weight training, sports and more. And it's totally free