The idea of browser extensions seems a good way forward and I did a little bit of digging and in Firefox there is a function in Help called ‘Report a broken website’ and it includes an option on accessibility see http://support.mozilla.com/en-US/kb/New+Accessibility+features+in+Firefox+3#_quot_Report_a_broken_website_quot_tool_now_has_an_Accessibility_option .
What it does not explain is what happens to the report so I have put in a support question see http://support.mozilla.com/en-US/forum/1/694766? .
I think we would have to extend this function so that it was specific for accessibility, included the email address of the user and maybe had some basic tick boxes to define the type of problem. But in principle it shows that reports could be generated within a minute.