Hmmm, this is actually a complicated question for me, for two reasons.
1) I work in the hospitality industry, meaning restaurants and hotels (restaurants for me). In my experience people who work in this industry often are more genuine, both with guests and coworkers. I still don't think it's the best idea, but it's definitely better than running over to the next cubicle and asking for a date. You get to see each other interact with others on a daily basis and see how they handle themselves in a variety of situations that you just don't see in any other industry.
2) I am eventually going to open my own restaurant/cafe. The guy I have been dating for weeeeelllll over a year now wants to be a part of that future and that dream, and I want him to as well. Whether we will be co-owners or owner and manager, or some other configuration of positions (hehe!) we will both be employed at my restaurant, making us dating (or married?!) coworkers. I think this is the absolute ONLY case where it is actually okay to be in a romantic or sexual relationship with a coworker.
Sorry for the rant ^^;;