I like Strava a lot but must disagree with those who say the premium membership isn't worth it. It's a matter of what you want I suppose. I consider the power estimates nearly useless but other features are fun and useful. I like getting my suffer score and following other local riders has given me some great ideas for routes I had not thought of before.

The iPhone app isn't as complete as the full web version. I use a Garmin to generate the data.