Our Chief Software Engineer, Dave, was recently asked by a friend if she should choose Mac or PC for her next computer. He had this to say:
Mac if you have any work to do, PC if you want to game, do 3D animation/CAD, or code in .NET.
Forget buying brand new, I've always bought refurbished without issues, as it saves a few hundred dollars. Though Macs are fairly price-competitive if you match components and hardware specs.
Macs don't let you customize the interface nearly as much as Windows, but if you ever need to go "under the hood," OS X is far more powerful. (see: Terminal) Also, Adobe software is far snappier on my MacBook than my more powerful Windows desktop. (Adobe heavily optimizes for Apple, and vice versa.)
Our office is all Mac for one simple reason: support. If something goes wrong with a machine, and we can't fix it, we scuttle over to the local Apple Store. While most "Geniuses" aren't much better than Geek Squad, it's still the manufacturer's store, so getting a computer or part replaced is significantly easier than trying to go through a third party like Best Buy.