I have been on many rafting trips, the most memorable was going down a class V in a four person raft. It is a great vacation to plan with a group of people, very fun and fairly safe. I would recommend paying the extra money and getting down to at least a six person raft. I have also gone on a class IV river in a ten person raft and it really detracted from the excitement. I liken it to going over a speed bump in a tank.
Most of my whitewater trips have been in the West Virginia area; although, I've also rafted in California, Arizona, Costa Rica and New Zealand. Rafting has given way to a new love, kayaking. On one of my rafting trips, I took a day long kayaking trip and was hooked. But that is another page...
Here is a picture of many people falling out of our raft while hitting a class IV rapid. I am the one in the front still paddling while all of those slackers are taking the time to fall in the water.