RunKeeper Pro has lots of social options, allowing you to share your workouts on Twitter and Facebook. It also allows you to control how much you share. You can even turn on RunKeeper Live so friends can track your progress as you go. (Might be fun for a big race, but a little creepy otherwise) You can set prompts to announce your progress as go, based on minutes or miles. The voice on the prompts sound so much like Oprah too, I find that really motivating!
RunKeeper has taken it a step further and also offers Fitness Classes to help you train for a 5k, Half Marathon, Full Marathon and Fat Loss. The classes cost extra, from $4.99 to $19.99, and are similar to C25K coaching and take you through multiple weeks of runs. If you sign up for Run Keeper Elite ($19.99 a year) you can get additional reporting and tracking of your workouts. Kudos to the RunKeeper team for finding creative ways to bring in revenue.
RunKeeper Free has very few features and is pretty basic. If you want a free exercise tracking app, then I recommend Cardio Trainer. Remember RunKeeper Pro is FREE until the end of January!