I suspect that 1) alcohol's subtle effects last longer than assumed--in much the same way caffeine withdrawl can last for weeks; and 2) it affects your working memory.. reducing it maybe 10-15%.
I don't think you would notice a 10% decrease in your working memory unless you were working on a particularly difficult problem like I was at the time. Depending on the difficulty of the problems you're working on, it's entirely possible to code while drunk.. But if you've ever tried writing filesystem code, vm subsystem, or another hard problem, being under the influence can make it impossible to make any progress. So there's a wide range, and alcohols affects may not have much impact on the work you do.
I would like to see it studied.. I just thought it was interesting that cossatot mentioned a similar affect from alcohol lasting a similar amount of time.
(This obviously also depends on your body type, how much you've eaten beforehand, etc as well)
I tend to drink one glass a day, but also take occasional breaks, and personally I haven't noticed any differences in ability and performance. I've also taken 1-2 month breaks from drinking (without issues -- always good to test once in a while!) but it doesn't really increase or decrease my ability.