I think many DJs make the mistake of catering ONLY to the young folks who hog the floor. I make a point to never do more than 3 songs of the same genre in a row, so I can involve the entire room, and not just the barefoot, red solo cup crowd that would dance to the beat of a freight train, given enough chemical stimulation. The old folks like to dance, too and it's sad to see them huddled in the back, stuffing napkins in their ears to drown out the din while the boom, boom, boom rules the room. Weddings are for all generations ... not just the bride and her friends. It takes a watchful eye (and ear) to connect the generations on the floor, but if you can ... the room will truly come alive TOGETHER.

DJ Pet peeves:
1) using WAY too much bass
2) playing 10 minutes or more of any one style, especially a non melodic type (EDM)
3) not including songs for all the generations present
4) failure to "connect" the crowd with minimal banter, witty intros, and special dedications

Just my thoughts.