I saw a really good article about absinthe on wired today. You should read it, even though it doesn't directly answer your question.
linky
I've had experiences with thujone, which is an active ingredient in absinthe, but never with the real stuff. It's a stimulant, and with alcohol makes you feel drunk but without the groggyness you might usually feel. Many people describe the absinthe drunk as 'lucid'.