Since I work in a hotel and served dinner/drinks etc at about 23 weddings last year... I can't see wedding ettiquette and not comment.
So, people who are planning to get married...
First and absolutely foremost. Either make sure the DJ you hire is good, make sure that if the DJ is from the family that he's been groomed into the position with a proper taste in music, or at the very least create a list of songs you DON'T want played at your wedding. Noone, anywhere, ever, wants to hear ABBA at their wedding. Neither do the staff.
Second, if you randomly decide to invite 50 extra people to your reception, do everyone involved a favour and tell all the people who need to know this information that will have to make accomodations. 50 dinners don't just spring up out of nowhere, walls don't randomly push back an extra 200sq feet, and not only will you manage to irritate the hell out of staff (which you will, who will then in turn make your party suck), you'll also be irritating your friends and relatives by cramming them into a small space and not delivering the promised product. This is noones fault but your own; either stick with your finalized guest list, or do everyone a favour and give the necessary notice earlier than 2 hours before the reception.
Also, if you or one of your guests should find themselves wanting to get a bunch of minors drunk, hold the reception at someone's house and not in a public facility. Buying drinks for them somewhere with a liquor lisence is a good way to get everyone cut off, and possibly have police intervention. This does not make for a fun party. Similarly, if your guests are rowdy drunks, please ensure that they don't assault staff.
Most importantly of all; drinking and driving is a no-no. Either make sure people have somewhere to stay, or make sure that they don't get face-down falling-over drunk off their ass. Nothing says 'congratulations on this special occassion' like having a friend or relative die - yes, it will be their own fault, but that won't make for very happy memories at your 20th anniversary party.
... okay, well I exaturated somewhat to make those arguments, but you should get the point.