Th security token errors should be more user-friendly. Instead of dumping the user into a rather useless error page with no other navigation, first check if the user is logged in. If they are, then renew their token (so their subsequent submission with be valid), and then take them to the preview/confirmation page of whatever it was they were trying to do, if there is a confirmation page/preview available for that action. This will accomplish two things: Protection agains CSRF attacks will still be there, because the user would have to consciously continue with the action to actually submit/save it, and second it will be much more user-friendly.
I often open dozens of threads/PMs/ etc in tabs and leave them open to remember to respond to different things. When I get around to responding I don't always think of the security token, thus I get the error quite often.