I have been to, what feels like, a gazillion weddings so I've seen it all! I think it really depends on what kind of reception you want to have. Are you just looking for nice background music or are you hoping your guests hit the floor dancing for 3 hours? Most of the weddings I've been to have DJs, cheesy and non-cheesy. I knew some people who decided to save money and not use a DJ, therefore making all their own CDs and relying on friends. I think this is okay if you have a lot of time prior to the wedding, but if you're deciding to do a LOT of things on your own to save money, do you really have time to put together enough music to cover 3 hours? These people didn't so they were still gathering music the morning of their wedding, the DJing friend was unreliable, and it flopped. The other good thing about a DJ or band leader is they can keep the reception flowing
The best wedding I went to had a string quartet during dinner, then after dinner there was a big band. It was great and EVERYONE was dancing!