Definitely lots of tail winds in September when I rode Tillimook OR to San Francisco in 2011. Don't ride northbound! I felt so sorry for everyone we met going in that direction mashing into constant headwinds!
Regarding traffic, it's actually pretty awful. I am not an experienced tour cyclist, only having done a few months in central Europe and this one coastal ride, but I gotta tell you, the constant traffic was a real downer and most of the towns along the way were just not all that interesting. Once you've seen a few dozen, you've seen them all. Same thing goes for the coastal views, too. Great the first week or so, after that... same 'ol thing, if you can even see the ocean through the fog. Again, comparing to touring nirvana in Denmark/Germany/Netherlands so perhaps the comparision is not fair - it's a completely different kind of tour. The only reason I continued this ride was the awesome people I ended up riding with every day, that made it all totally worthwhile, and the desire to not wuss out
The camping was great, too, a never ending string of pretty good state/county/etc. parks, but while I was riding many were in the process of closing in CA so be sure to check the respective websites re: park closures, the last thing you want to do is finish up a long hilly ride to... a closed park and be forced to continue on. I had great mobile connectivity so checking the websites for closures any time I wanted was easy.
If I was by myself I would have quit and gone somewhere else, the traffic was just no fun at all - it's not like you are meandering on lightly traveled back roads at all. I got on the road right after labor day and during a week or so afterwards the traffic was heavy but died down after that, so I'm not complaining about the holiday traffic, I expected that. Really if you can avoid labor day and even the week before and after when it's ramping up and slowing down... much better. It's just sucked with constant RVs, cars, and logging trucks zooming past you. I had very few safety fears with the RVs and tourists - they always gave us a wide berth. It seemed like it was the locals in their pickup trucks and the logging trucks that would blow by with inches to spare. I finally got less nervous about the logging trucks as time went by - they are pros and they know exactly how far away from you they are, but still - scary stuff when they pass so close, not to mention the wind blast. I also got less freaked out about taking the entire road when it was, in my expert judgement in road sharing, just too narrow for cars to pass us safely to stop idiot drivers from trying to squeeze past - you need to protect yourself and get right out there when it's not safe - people are insane so you're in effect protecting them from a head-on collision when they try to blow past. I saw one too many close call head-ons before I started taking control of the situation and only letting cars pass me when *I* judged it was safe insead of the other way around. Scary incidents decreased dramatically after that
Ditto for the few narrow bridges you will be forced to cross in the road - I recommend earplugs or loud music to drown out the drivers screaming "get off the road!" like you have no right to be there blocking traffic on a super narrow lane (as if they expected you to swim across the river with your bike or fly across like superman or something, go figure).
In the end all the stress from the safety threats, close calls, careless driving, exhaust pollution and hassle of the traffic just wore me down after a while. Yah I'm probably spoiled by riding less traveled roads/paths, but there you go, one person's viewpoint.
Riding in San Francisco was pure joy. By then the hills in the city were nothing to me and it's such an uber awesome city (including the surrounding areas) to cycle in. We rode into town directly to Tour de Fat http://www.sfbike.org/?fat
which blew my mind for sheer 2-wheel loving awesomeness. And the northbound train goes through SF so that was a convenient ending point for me
The drivers are in total harmony with bikes on the road and knew exactly what to do. Never ever felt at risk or that I was in any driver's way in SF. If I was single I think I'd be seriously considering moving there, really, it's heaven