The above posts seem mostly dead-on about the lower. I've only boated that once also, at around 300 cfs. It is a long, fairly isolated stretch with alot of flat and class II. The biggest hazards were definately the fences. I recall 5 or 6 fences, but they were generally easily recognized and portaged. We did have some bulls run along the stream bank just downstream of us, then ford the river as we were approaching. Nothing like several 700 lb. slabs of beef blocking your passage!
We did see some landowners in the upper streches, but they were family types and the kids waved, etc. The reservoir is at the end of the run, but takes its fair share of time and effort to paddle across.
I'd say its worth the time once or twice for the change of scenery, if you can take the run for that and not for the excitement.
gage: North Fork Poudre at Livermore
I would also be interested to hit the upper section some time, but have no beta....