This seems like a no brainer, but based on some stuff I've seen on Linkedin and Twitter in the last few days, it clearly bears repeating:
Don't put anything on the social web that you don't want potential partners, customers, employers or even romantic partners to see.
I've seen a bunch of posts from people bitching about the job application process (some even naming employer names) and trashing interviewers. One of the former was on a group page in Linkedin. Since the poster is looking for a job in PR and the group is for PR people (with an active job board), it seems unlikely that after reading his post anyone from the group would be interested in hiring him now. Poor guy.
I know it's frustrating as Hell to be looking for work right now. I'm living with it in my own family. But I don't think complaining about it in a public forum is a very smart idea. With fewer jobs available in the first place, people don't need additional reasons not to hire you. And nobody's still naive enough to think recruiters and hiring managers don't surf the web for you, right? If you've posted this kind of thing publicly, consider investing a little time today in taking it down.
It's impossible to stay positive all the time, especially when you're seeking employment in a bad economy. But reserve your frustration for a more private setting. You'll probably get a more satisfying solace, and it won't do damage to your public reputation.