I don't get too serious too often, but I still believe work functions should still have some boundaries, I mean, you have to see these folks again the day after or a few days after most of the time.
I care what my management and coworkers think of me, so going wild at a business functions is totally out of the question for me. I might have longer, general conversations with folks I don't normally get to talk to as a regular person, but drinking to much is totally out of the question.
Sometimes I think folks who have a desire to take advantage of the free drinks and see getting really drunk as having a good party, know that it doesn't look as good if you they are the only ones doing it, so trying to get others to do the same is a must !
People may not ever mention it to your face at work if you show your @$$ at a company function, but they don't forget it and they will quietly judge what kind of person they think you are. It's human nature.
Decorum at work functions (work in general) is important I think, one never knows when prior nutbaggery may come back to haunt. The lure of free drinks is difficult for some to deny I guess, but it's not often going to go well, as in the case I mention here.