I struggle with this too. Where I work I can switch between Dell Latitudes and a MBP 2.4 pre unibody. I'd get mad at one, and grab the other for a few months, then switch again. Been doing that for 3 years or so. Now I'm finished. I am back with the MBP to stay. And probably will actually pony up and buy a new MPB. The Dell with Win 7, which is really very good, took 45 seconds or longer to come out of sleep. The MBP? About 5 seconds. Plus I had the cursor stop at random for about 5-10 seconds then come to life again on the Dells. All the hardware was fine. I did a clean Win 7 install a few times. I still had these pauses. Not sure what the thing was doing. Now the MBP isn't perfect. I see some beach ball time. And some things are easier with Win7.
But at the end of the day, the MBP won. One thing I do note, is the MBP I use is 3 years old, and it seems to run better than the Dell which was new in a box over the three years (D800, 820, 830, E6500). The Mac stayed consistent. The Dells I have had slowed over time. I really feel the 2007 MBP I use run faster and leaner than the latest Dell Latitude.
I can buy a new Dell, and a year later, I'd want to replace it. If I buy a new MBP, I really feel I won't be feeling the need to upgrade for at least three years. that helps offset the outrageous price difference between a Dell and an Apple.