Two of my room mates and I all have beards/goatees. As you can imagine, there's a lot of shaving done in our sink. We learned the hard way that washing tons of hair down the sink drain is a great way to clog that bad boy.
We called Adams Plumbing and Heating and a plumber came over the same day. He used a plumber's snake and had our clog fixed pretty quickly. He was a pretty nice guy, although I thought the bill was a bit steep.