THC, being soluble in alcohol, will evaporate away along with the alcohol in the extract. I'm not positive, but there was some mention of it in the "Nugs dipped in cognac" thread. What brand have you used, if you remember? I used some cheap generic stuff. How much did you put on the weed (per gram, per bowl, whatever)?
dude, thc will dissolve with the alchohol, but not evap. the thc extract is whats left after the alchohol evaps.