I have a windows 7 system configured with an Intel i5 and 16 gigs of ram as my main work horse, and a macbook Pro as my secondary portable system for lighter work. The macbook is very underpowered for some tasks I need out of a computer, but does well enough for lighter work on the go.
Personally I could never stand to have just one system, and so the desktop will continue to receive updates every few years as required. I really don't see the point in paying out the nose for high performance laptops either. They are hot, cost several times that of similar specs in a home built desktop system, and high horsepower systems tend to have crap all for battery life.
Unless you normally find yourself on the move most of the time and need to work anywhere, then I would say focus your funds towards a solid desktop system, and pair it with a low cost laptop. I would Not suggest apple unless you are planning to work with developing for that platform. The only way I justified the Macbook Pro was because I needed a portable system for photography and astronomy work, and was planning to pick up the cheapest option for a mac that I could to get more experience on the platform. Given that I already have a vastly superior desktop that would be used for anything I needed while sitting at my desk, buying a mac mini and a 800-900 laptop did not make sense.