Thanks for the feedback, all.
Yes, the site would target those planning and joining multi-day river trips. It could still be used for dailies, but would probably indeed be overkill.
I realize that if it's not easy to use, people won't bother, so that will be foremost in the design. Once I get to a point where it's usable, I'll send out invitations for people to sign up, check it out, and make comments/suggestions. I'm happy that there's interest and could provide a useful service.
On a related note, I need a name for the site. Here are a few ideas:
Picture a .com or .net at the end. These are just ideas; mostly inspired by the sister sites
of backcounty.com, like SteepAndCheap, TramDock, etc.