I am Mac user and have never thought of myself as "below average user". Considering most design, sound and film post production is done on Macs, below average seems a bit of an odd descriptor.
maybe below average is stretching it a bit far. but word,web browsing,itunes,and photoshop sum up the bulk of the MAC using community.
the niche market folks that are "designing with Illustrator, Flash and Photoshop" are using a MAC because its what they were told to use. they ask around and people will tell them " Mac's are better for graphics " which is both a truth and a myth because both mac's and pc's have the same programs. The next part of so called graphics is color output of the users monitor. because others are using mac's lets assume all mac screens are built exactly to the same specs and every picture looks that same across all Apple monitors. for PC users because there are so many options and different brands to choose from not all monitors are created equal especially now with LCD's this point is fact.
Now when it comes to 3D and more intensive design work look at the Autodesk line of products which soon will come to a MAC have been done on PC's for a very long time.
so why do people use mac's for sound? the majority of mac users for sound design purposes ie, unsigned talent, singers, bands etc use Mac's because of some of the programs available on a mac that are extremely cheap and extremely easy to use. i mean easy like you run and off you go easy. because they are artists not computer geeks. and they dont wanna blow a whole bunch of money to learn how to use programs like Pro Tools, which is both on mac and pc.
people that have problems keeping PC's secure, virus, spyware, spam free and need to contact tech support are the ones who need to go out and buy a mac because they simply just dont know how to keep them secure or dont want to pay someone to let them know. they go and grab a mac because they hope because so few people use mac's that they wont have any problems.
Bottom line. when you compare the hardware and the cost of performance Mac's will never have the same performance as a PC. dont beleive me ? dual boot any intel core 2 duo power mac with windows xp or vista. run a few benchmarks. the mac isnt going to come close.
I will admit I'm a hardcore Pc user. I've used MAC's before back in the G4 and G5 days while i was in college learning graphic stuff. I hated the stupid mouse it came with which was clearly designed for looks and not function. and compared to the cheap PC i had built at home the mac was pissing me off with how slow it was compared to my cheap lil PC. cheap because i built it myself and selected only mid-level components being a student on a budget.