Hey
I'm another Fetch user! I tried the Serpentine log thing for a while before I tried Fetch, but as a relative beginner I found that the community thing on Fetch was a big spur to keep me going out.
As for running logs in general - I used to run a couple of times in a week, and then fall away from it, and go for months without, feeling guilty and then getting enthused for a week or so - and so on. Until I started recording my runs, that is - it's a great motivator to see your self improve over a course, or be able to run longer/further!
I'd also say blogging about your runs is a good indicator of how far you've come. It also helps you identify patterns etc in your training. I use a different one, but I think I'm right in saying that FE has a blogging side to it?
xx