[phogster]

Anyone else compete on these types of sites? Are they worth it?

[yankoff]

Have been playing with their contests since I finished ML course on coursera. I think they worth it, pretty fun and addictive, plus a very good way to practice your machine learning/data mining skills. Community there is very good and helpful.

[SuperChihuahua]

It's "easy" to get a good ranking so it looks good in your cover letter :P