I had an earlier thread http://priuschat.com/forums/gen-ii-prius-care-maintenance-troubleshooting/70763-help-remove-wiper-arm-nut-part-number.html but this topic may worth its own. I contacted a dealer about the wiper arm nut and was warned that the wiper arm base is made of "soft material" such that when it is installed the grooves got cut into it and if the wiper arm is removed then the grooves will be destroyed and I will need a new wiper arm. This may have been the reason why I wasn't able to pull the wiper arms off by hand. Any 2009 owners out there removed and replaced their wiper arms yet?
Thanks! Have you removed your 2009 wiper arms and put them back on? If so what's the production date of your 2009? Mine feel like really stuck on which is consistent with what the dealer said.
I have not removed them on my '09. I did on my '04 and they were difficult to get off the spline. You have to make sure you pull them straight off the shaft and not try to pull at an angle.