I was just checking when this poll would close and got curious on how the cooling choices have changed over the years. The original poll posted by eobard back in 2005-2007 ended up with air at 72.12%, water at 25.12% and Other Cooling at 2.76%. For the 2008 poll thread, air picked up to 78.50%, water dropped to 19.11% and Other Cooling dropped to 2.39%. And this poll thread (2009) is presently standing with air dropping back off to 76.50%, water gaining back to 22.25% and Other Cooling losing back to 1.25% with only about 16 days left until the poll closes.
I am theorizing that back when eobard first posted the original poll, air cooling was butting into a cooling wall because that was right at the very start of heatpipe use and water was more efficient at the time. By the time 2008 rolled around, heatpipe heatsinks had gotten very efficient and were actually cheaper and easier to set up than a good water loop. Finally, with the 2009 poll, we are seeing water again gaining more popularity, probably due to the tremendous heat output of i7 processors when highly overclocked. At least that's what I think is happening. As for the more extreme cooling options, I guess they are just steadily falling out of favor.