I have one facebook friend who is constantly spamming her status in order to win competitions. The main point seems to be to get people to the company's page, and "like" it. She's basically begging all of her FB friends to look at something so she might win a prize.
Another method used is to ask participants to tag themselves in a picture, which usually has ad copy, so it shows up in everyone's news feeds, and also the participants albums.
Recently I've seen an ingenious but even more annoying method of badgering FB friends... write an app that autonomously posts to their news feed 2 or 3 times a day. No need to keep egging on participants to spam their friends via their status, it's all done automatically from within the app, since it has posting privileges.
I've only seen one so far. Now imagine what happens when someone has 5, or 10, of these apps installed, and they're each posting a couple of updates per day that all of their friends have to see...
I wonder if this is even permitted, since it's just spamming a company, not actually providing any useful update content...