Holy shit. I tried the filter on some Skyy vodka I had in the freezer ($20 a liter - really not a terrible vodka to begin with), since it was what I had lying around... and oh my GOD what an incredible difference. I had about 300ml left in the bottle to work with, and I reserved around 30ml in a glass while I poured the other 270ml or so through the filter twice. It really didn't take very long at all (although admittedly I wasn't waiting around uber anxiously for it), and after the second time through when I tried to do a sample... good LORD was it ever an insane difference. The filtered stuff is gooooooood. I wondered if I was imagining it, but hey, that's what the reserved fluid in the glass was for... and man oh man, Skyy really isn't bad to begin with, but the HUGE difference was obvious in tasting even a touch of the unfiltered. I went back and forth a couple of times with small sips, and there's just no doubt about it... the filtered stuff is vastly smoother. It really would go down like water if poured over the rocks; even neat and at room temperature it was pretty hard to believe that was 80 proof liquor I was sipping.
And no, it isn't that the filter's pulling out the alcohol... I poured the stuff back in the bottle it came from, and there just wasn't any visible product loss. To make a serious impact in taste to 80 proof liquor based on alcohol level, there would have had to have been a VERY obvious impact on the overall fluid level, and there wasn't.
Anyway, now I'm SERIOUSLY excited about the real experiment - trying the same thing with Early Times, the world's crappiest bourbon. I'll keep you posted. =)