We do, and it is needed here. I hate regulations, extra rules, "the man" always on our case, but if we didn't have limits on the amount of use and type of use on some of our pristine rivers, they would suck. I like to do rivers that aren't permitted and regulated as much, but we have the beautiful Rogue here in Oregon that sees plenty of use, and would get trashed if there weren't limits on people and usage.
A popular river in the summer here is the Deschutes. When I was young, it was a "girls gone wild" college party/ drink fest with drunk boaters, drunk drivers, over use, and generally I personally saw it things get out of hand. Now even day trips require permits, and they watch the river very closely. I like it better there. I'm taking my 5 year old there this summer, and I won't have to worry about him seeing something I don't want him to see. I also won't worry as much about drunks on the road along the river.
Wishing I was on the river instead of surfing the web...