I've seen (and been in) the good, the bad, and the ugly, when it comes to relationships at work.
I personally think it's better if you at least date outside your unit. There's much less chance for drama that way. Also it is easier to remain professional. When my ex and I both worked in the same ICU, we would constantly nit-pick each other's work and get frustrated with one another. It was very stressing on the relationship.
I know of a tech I work with who was dating one girl from our unit and another in the ER. Both girls knew about the other one... well one day (recently, I might add), both girls confronted said co-worker, and I don't think it was pretty