Definitely one of the best summer activities to take part in here in Phoenix! The water is cold and provides a nice break from the summer heat. Depending on where you launch into the river, it can take anywhere from 2-4 hours to complete. Tube rentals are rather reasonable but don't try to bring any glass bottles with you!
Not only is it refreshing, it's also relaxing (if you want it to be). You sit in the cool water, soak up some sun, and take in the surrounding landscape. If you're lucky, you'll see some of the wild Salt River horses.
It does get rather busy and congested, so I recommend going earlier in the day. We usually go at around 9am and finish right as it starts to get busy. If you drive yourself and don't take their buses, be sure you have a car at the end of the river. They buses won't take you unless you can pay right there. The Maricopa Sherriff's office won't provide a ride either. Trust me, don't get stranded!