LASTFUTURE The interface is very intriguing. Sure it's only made for temperatures but it does that very very well, and way faster than fumbling around with a full fledged units converter. (Version 1.1)
CHAS_M This functionality is already present in the (much more handy) conversion widget, part of every Mac OS X desktop for years now. The slider idea is cute, I guess, and you can't complain about the price -- but can't really see any point to downloading this when I already have a tool that will convert not just temps, but currency, volume, distance and a dozen other measures just as easily. (Version 1.1)