Does anyone have any experiences with these services like gollum Network? Is it safe? Does it earn you a net monetary gain compared to your electric bill? I have a pretty nice desktop that sits around for most of the day, just wondering what else I can do with it while I’m at work.

Please note, I’m asking specifically for people who have actually done this and what their experiences were, good and bad. I understand I’m not going to make tons of (or possibly any) money or start a business.