At the office I work on a high-end Dell Latitude E6500 laptop. It's a nice machine with all the bells and whitles including eSata, FW, SC card slot, 1920x1200 display, and I run it with another 24" Samsung display.
In order to put what I like about the Mac Pro in context, I use to build my own PC's. My last one was a highly custom water cooled system. It had SLI, dual PSU's and a three loop cooling system. I invested over $6K in that system. If you follow custom PC building at all, you will know that cable management, low noise cooling, and internal aesthetics are paramount to build a reputable rig. Of course it was overclocked to the extreme... the Q6600 was overclocked from 2.4GHz to 3.6GHz prime stable for 12 hours. However, it was plauged with issues related to the poor Nvidia chipset, poor Nvidia drivers early in Vista's life, and even instability when gaming in SLI well into Vista's life.
So when I decided to move to the Mac Pro, things that I really appreciated about it where the attractive minimalist design of the exterior, and the beautiful and thoughtful internals that only a PC modder can truly appreciate. Things like cable managment in the Mac Pro are almost non existant because Apple has integrated so much into the main board such as PCIe GPU power traces on the main board, back plane SATA connectors, integrated Wifi and BT. Even small details like the PCIe card retention mechanism are amazing. The CPU tray is a dream and very elegant design. I've also never seen air cooling as quiet and well executed as I have in the Mac Pro. While the fan speeds don't ramp up fast enough for my liking, it's still a very elegant and quiet design.
When it comes to the OS, Windows is perfectly fine and Win 7 is actually reasonbly attractive, but I still find Vista/Win7 to be gawdy "look at me" designs that make the OS the center of attention. OSX is understated, sleek, minimalistic and lets the task take center stage. It's a breath of fresh air. OSX says I'm all about getting work done or letting you do your task. Windows says you need to tweak and customize me and screw around to get anything done.
Now, obviously I don't get the benefit of working on a Mac for my job, but I spend a lot of time every evening on it using Aperture and to a lesser extent Final Cut and it's just a dream to work on.
Apple makes complex things simple. Syncing all my machines and my phone through MobileMe is a killer feature that simply doesn't exist on the Windows side. Automated backups to my TC are just so easy. Buying a new Mac or doing a clean install from a TC backup are just so painless it makes me laugh how onerous of a process this was on Windows.
Anyway, I could go on and on (obviously

)... but the fact is that Apple has made my life so much easier and let me focus on being productive and I don't miss all the expansion options and headaches with drivers that came with maintaining a Windows machine at all. Sure you have to assimilate with the borg and do some things the Apple way sometimes (it's futile to resist) but the rewards far outweigh the small sacrifices in my opinion.