The words "open bar" are music to every wedding guest's ears. What's better than attending a wedding, having a good time, and getting drinks for free? This however this does not mean getting you should get extremely drunk, cause a scene, or having to be carried or escorted out of the reception.
The bride and groom have an open bar so that guests do not have to worry about bringing money or credit cards with them and as part of their "Thank You" for sharing in their day. Although this is very nice of the bride and groom, guests should not take advantage of their generosity.
What people might not know is that in some contracts, the bride and groom have to pay for every drink consumed. As you can imagine, this adds up pretty quickly. Other contracts charge a flat rate for an open bar per hour which is also costly. There is also ALWAYS a "NO SHOTS" policy to help try and prevent this from happening. I am not saying don't drink, just don't drink excessively. You don't want to be that guest that has to be carried out to the taxi (believe me, it happens more often than not). I was always told growing up: have fun, but not too much fun.
I think that this is very applicable to a wedding reception with an "Open Bar". Don't you want to remember your friends' wedding reception anyway?