So far I am very pleased with the Runkeeper App. I have the free version. I think when Apple iPhone OS 4.0 comes out, the App will be a lot more useful due to 4.0's ability to multitask. As it stands now, in Runkeeper, the App will stop working if you get a call or attempt to execute some other type of iPhone activity. Nevertheless, you can pause the app and return to the homescreen and then resume the app without losing the current activity data.

I think this app is useful for both recreation, training, rehab (currently I am rehabbing my Achilles tendon injury). One of the most useful aspects of Runkeeper is after your activity, you can send the data from that session to the Runkeeper website and it will create a full-screen size page with stats, graphs, pictures, etc., to help you analyze your workout. You can do this in the free version.

Overall, I'd rate this app a solid "A".

Here is a screen shot from my walk today on RunKeeper's website: