There were several times when I was bored in the OR during my 3rd year clerkship. I remember one case that lasted about 9 hours, most of that time I was retracting and could not see what was going on in the operative field. I recall looking at anesthesia, sitting in a chair, reading, and thinking hmmmm....who has the better deal here?
However, the times I got to do stuff in the OR it was absolutely fantastic. Even stuff as simple as suctioning can make you an active participant (on vascular anastaomoses, believe it or not, suctioning is a very important part and requires a bit of finesse to do properly. And as I did my 4th year electives and was allowed to do more in the OR, it quickly became clear that there is nothing else I'd rather do. My back ache doesnt' matter when I'm an active participant in the case. And I've been allowed to DO a number of cases. Add to that the other procedures (lines, chest tubes, bronchoscopy) that I've been able to do and I'm totally hooked.
There IS more to being a surgeon than the OR. I'd say you have to like most of it. You have to learn surgical judgement, when to operate and probably more important, when NOT to. You have to take care of patients post op and any complications that develop. Also (at least at my institution) surgeons are probably called more than anyone else to clean up other people's messes. Surgery is about efficiency and getting things done, and as triathelete 411 said, surgeons tend to get bored when they aren't doing things. If you feel great pain, for example, during loooooooonnnnnnggg medicine rounds, you're probably a doer and something surgical is a good fit for your personality.
I'd say it's fairly normal to be bored in the OR under circumstances when you are retracting and can't see (ie when you aren't an active doer) However, if you were bored when you could clearly see the operative field and had some active role, then perhaps surgery isn't for you, or perhaps one of the subspecialties would float your boat. One way to find out is to do an elective early in the 4th year. That way you'll enjoy the privleges of being the senior student and likely would get to do more. I wouldn't cross it off your list just yet.