I've been using strava for about 6 months now and love it! It's a great way to stay motivated, especially in the off season. Earning a "King of the Mountain" is pretty rewarding and addicting. The new segment explorer tool that they added last month is great for finding new segments to test yourself on... I haven't experienced any problems regarding it not recognizing my tracks with my iPhone 4.
http://app.strava.com/athletes/147576