Paul Stamatiou is more productive on a Mac. Why? The combination of Exposé, Quicksilver, and Spotlight. These three things taken together really make the Mac a powerhouse of productivity (and I should know since I use the very same tools, though I tend not to need Spotlight that much. I'm just that good).
Now, I spend a fair amount of time using Windows and it isn't an awful experience (Windows is good for some things), however, whenever I am on my Mac I feel like I'm getting more done.
So, TUAW readers, share your productivity hints in the comments so that we can all become dynamos of productive power!