Did it on singles last year.....we were so inspired by all the families and tandems that we just bought a co-motion for our 6 year old and dad so that we can do multi-day rides in other states as a family....
You MUST EAT PIE. and Homeyba is correct, it is a rolling party. The route last year was southern, and it ISN"T flat. I've heard the northern routes are much flatter. We lucked out with weather, it was cool the whole week. Sorta made up for the hills. RAGBRAI has it's own forums, it was fun to participate in them and then meet some of the regulars face to face during the ride.