Co-Worker lovin'

I always wonder if getting involved with a co-worker is a bad idea or not. It just seems so easy to get caught up in someone you are around all the time if they are fun, nice and attractive. why not right? I just can't help myself. I am in my twenties so its not like I am in a corprate office of some sort, just a restaurant. I was just wondering, are co-workers off limits? Or can that line be crossed sometimes or exceptions be made. What are your thoughts on the taboo situation.