I've flown the T-38 a few times while I was in the US and a one degree temp change could mean to difference between stopping on a aborted take off or going for a X-country drive off the end of the runway. ie accelerate/stop distances. Guys who had flown for a while would also note the dew point, as they knew that it is relevent and that it does effect your aircraft performance.
I'm sure that with most aircraft the difference is neligible. However, the Dew Point does effect density altitude and does effect aircraft performance. Just ask any old 104 drivers out there if they thought about it. I'm sure they will say it is an "indicator" of decreased density altitude just as I have mentioned while trying to answer Lump Jockey's question.
cheers
Ps here's a better URL to go to
http://members.aol.com/matt999h/beer.htm