One thing that hasn't been mentioned in this thread, that I think is important, is learning how to read the water. Being good on the sticks is important but knowing where to row is more important. For beginning boaters, take the time to stop and look back upstream after running a challenging stretch. It is much easier to see the route from below than above and it helps to correlate what you saw from above with what the rapid is actually like. This is why the guides can gracefully manuever through the rock gardens. You can't possibly memorize the route through every rock garden, you must read it and row around the obstacles as you go. This is not that hard to do, but you must learn by experience....one trip with a guide won't teach you how to row the Sol Duc.

Complacency because you think know the river is another common cause of accidents (ie the Hump is easy.... except for that new log!). Unless you've floated it since the last storm you don't know it and must read the water and determine what's safe and what needs to be checked. Upper Sauk is the best example of this per the previous post. I've run that stretch many times and sometimes didn't have to get out at all, but don't hesitate to, if I can't see a safe way through. Fast water going into log jams is particularly dangerous on this stretch, but it changes with every high water.
Never assume there is a safe route!

Summer Run this means you! The lower Hoh will change dramatically with every flood and then you don't know it again. With the cautious nature and willingness to learn that you have exhibited on this thread I am sure that you will be able to float it safely again.....but not because you learned it.
Hope this helps.