Tubing's a blast. We used to do the Rio Grande at least 4 times a summer. Huge groups, we had about 30 truck tire tubes, and rafted them up to a 15 man navy surplus life raft. The life raft had no room for people, full of beer coolers. So we'd have about 25 shit faced drunk chemistry phd's and grad students floating for a few hours. Some marriages happened as a result over the years.
Big fun, but a miracle there was never a fatality. (especially the drive home) Now it's more sedate and not shit faced drunk, but we do the river in kayaks at least 6 times a year. We have to cram it in though, since they only let the river run about 6 weeks a year now.