I've started logging my runs in dailymile.com late last month. I've been a member sometime back, but it was only last month that I've started to log religiously into it.
Prior to DM, I was using trusty Excel as my tool for logging my runs. It actually proved successful in monitoring my training for last Feb's Condura42k, employing a Frankensteined mix of plans from Runnersworld (for the weekly mileage target), reading RUN by Matt Fitzgerald, and alternating a twice a week hard run method (1 speedwork and 1 long run). The plan came up on the fly every week, so there was nothing fancy there. But logging the run itself was a good approach in determining how effective (or not) it was.
DM has the same logging mechanism: how much mileage/time you ran, where, and how you felt. There's also a description line if you want to add one. What's more is that your friends can add a comment/motivation to your run/training, similar to how FB allows you to comment on one another's status. Plus there's a donut and cheezeburger meter as seen above.
Well I only have 6 friends right now, so I hope those of you already in DM can add me up. The runs you log will definitely motivate me to do my part too. If you're not yet in DM, do sign up and add me. Click here for my DM userid.
Just don't cross-post your DM logged-runs in FB. Your non-runner friends might get irritated. ;-)