Forum Moderators: open
users never see them
the vast majority of first tier search engines totally ignore them
they add a few bytes to every single page you serve up
they show your competitors exactly which keywords you want to serve up
(even inktomi recommends not using them unless you have the time to write them individually for every single page)
did i miss something folks?
I am 100% sure, after reading there, you will come away with more answers than questions :)
Considering the pressure to conserve bandwidth in a busy forum, not delivering meta tag content to human visitors, might (theoretically ;)) make sense.