Ezra Klein speculates on the reality of the "beer goggle" effect:
I hadn't thought the beer goggles effect was real -- rather, I'd assumed the effect was a mixture of lowered social reserve (and thus reduced fear of social opprobrium) and higher horniness, which combined to overcome qualms you'd otherwise have about a potential partner.
In fact, I'm still not convinced the effect is real, and wouldn't be surprised to learn that it's a function of people being more interested in hooking up with each other, and thus mistaking attraction for attractiveness.
I'd say Ezra's onto something. Evidence: approaching thirty seems to have exactly the same effect. Followed by a sobering-up period as you observe what sort of marriages this seems to produce.