David Armano posted a great little Top 10 list regarding social media's dirty little secrets. Number 2 resonated with me the most, as about half my followers on twitter are trying to sell me something without engaging me. I take issue with number 10 however, I am still a sucker for top 10 lists.
The full list is worth a read.
2. Most social media is bad marketing/PR
Few organizations really want to engage with their customers. It's just easier to slap together a blog, Facebook fan page or hire someone to tweet about your products and coordinate events that hopefully generate buzz. Participation is hard.