My buddy and I have been using his, it comes in real handy while floating new rivers as you can mark the put ins/takeouts and know where you are in relationship to them every time. It is also handy for marking danger spots on rivers you may be less familiar...You can also determine the length of a float which, on rivers that wander or oxbow alot can vary drastically from the road miles...

Now, on a river I am intimately familiar with I don't see much point in it really.