Keeping a devlog isn't a requirement, but is a part of the Jam which keeps people updated on your progress and may help people see the effort you are/have put into your game.
If you are wondering what makes a good dev-blog, I guess a good place to look is at the dev-logs that won the best dev-log award in past Jams!
(10 minutes later...)
While looking them up, I've only found
3 4 results, one of which I can't see as the image is broken (?), so maybe it's best to just look through the game topics and check some out yourself and see what sort of style you like and get some ideas how you can make your own dev-log
Here are the three results I found (+ updated with Jam 10):
Jam 6 - TerraFriedSheep
Jam 7 - Team Ultimollusk
Jam 8 - Unsure, images appear broken
Jam 9 appears to not have a best dev-log?
Jam 10 - Coolbot4k
and I don't think the results are posted for Jam 10? Thanks Snail_Man for finding the post
Edited by TerraFriedSheep, 06 July 2013 - 03:10 PM.