Graphic Design
Mac ruled the graphic industry for many years in the early and mid 90:s. The main reason for this was that the applications used in the industry was only available for macs. This changed however and everything that you can get for a mac nowadays you can also get for your PC. In fact there are many things you can get for your PC and not for your mac.

The myth that Apple has hung on to the longest is the photoshop-filters myth. They still claim to beat the best PC:s avaiable with their top of the line systems. This has been proven wrong in numerous tests though and Apple's own tests are very poorly documented. Take a look at this diagram from Apple's website. Does it look like a serios test to you? Note that no specifications on how the test was done or any information about the PC used except the model number is stated.

This test can be found in "detail" here.

Benchmarks

Here are some tests that have compared a PC and a mac in photoshop operations.

In pro digital photography, megahertz matters
"What's there to say but the obvious: The fastest dual processor Mac has been soundly thumped by one of the fastest single processor PCs. If this report had included a dual processor PC, the PC's margin of victory could have been even greater"

Photoshop benchmarks
Editor's note: Test made with PS7Bench that consists of 21 tests such as blurs, rotations, masks, color filters and conversions.