IMO, based on what I've read about it over the past year or so, I think it's somewhat of a flawed concept, with an unfavorable enough overall risk vs. benefit ratio to not warrent using it.
Let's start with the vodka itself. It's not pure alcohol, only about 40% on average, there are many other things in there, like sugars, carbohydrates, ect. All of which will be an addtional nutrient load on the tank. While some of this load will undoubtedly be consumed by "good" organisims, the rest could become fuel for less desireable microorganisims in the tank. Also, please correct me if I'm mistaken, but doesn't the alcohol itself tend to kill bacteria? I sort of understand the premise for using it, as the carbon in it fuels bacteria, but wouldn't the complex alcohol molecule itself be antiseptic in nature in the tank? Somebody with a better understanding of biochemistry than myself is going to have to break that particular point down for me...
In addition, I'd suspect enough free carbon is present in most tanks at any given time to easily support adequate bacterial populations...
Second...let's look at the precieved benefits of elevating these bacterial levels in the tank. As Borneman and others have stated, there really isn't any concrete evidence out there that conclusively state nitrate's overall effect on corals, either positive or negative. The levels of nitrate commonly encountered in the average reef tank I suspect are likely of no negative concern. To the average reefkeeper, the focus then shifts from maintaining a healthy environment for corals to maintainging an envionment low enough in nutrients to keep problem algae at a minimum. Obvioulsy a desireable goal in the hobby, as none of us likes to show off a tank full of algae. but not a goal that is necessarily directly tied into the overall health of the coral.
We are constantly doing things to our tanks that affect bacterial populations. Skimming, water changes, feeding, introduction of reducers like macroalgae, added livestock, ect...all these things ultimately impact the bacteria populations in the tank. This, IMO, obvioulsy creates an inherintly unstable bacterial population, one that is in a constant state of flux due to our input. (I think that we are able to keep this flux in a range that creates a livable environment by not making sudden or drastic changes.) By tampering with these poputions further by using something like vodka, I feel you are doing nothing more than adding yet another varible to an already unstable situation. Overdo it, or mess it up, and you may have a flux on your hands you simply can't control.
Bottom line, I fail to see where the benefits of dosing vodka outweigh the potental risks...
MikeS