We ran this yesterday to scout it out. Lots of wood all over the place, but all of it easy to avoid if you are in your boat and on your line. We ran from the slalom course/watershed gate all the way to Lake Washington and didnt have to portage anything. Even the big log jam had a clear line through it, but it is definitely not somewhere you would want a swimmer or somebody who couldnt control their boat - lots of potential for something bad to happen.
The only other hazard is a cable spanning part of the river (described here:
http://www.kingcounty.gov/recreation/boating/rivers/cedar-river-cable-hazard-notice-2012.aspx). At lower water, it is clearly visible and easy to avoid on the left, but at higher water, it could be hard to see.