I have nothing against Macs as machines. I have a lot against Apple as far as their marketing goes and I have a whole lot more against people who want to talk about how awesome their Mac is.
First, Macs are compatible only with what Apple makes. If you want to switch from a PC-based network to a Mac one you have to replace almost every piece of equipment connected to the hub by any number of degrees of separation. Replace the cord to the router so it has the right jack on the computer end- but oh wait, maybe your router doesn't have the right funny-shaped jack that the cord does on the router end. Buy a new router (I know/seriously hope to god this isn't ever the case but I'm just using an exaggerated example). Oh wait, your wireless cards on your other computers not hard-wired don't read this type of signal. Buy new ones. Etc etc.
As computers, Macs work fine, though. Not much to really be said here. Not much in the way of high-powered hardware compared to most comparable PC's (due to Apple being the only people who make Macs and putting out a new version every so many years while almost every other electronics company is making some sort of computer and a new one comes out on a weekly basis from the collective whole of the computer industry), but they work fine. Just not as good if you're going to be doing a lot of really high-end graphics or movie work or going to be working with huge numbers and calculations (in which case you might want to invest in a math class, calculator, and/or supercomputer).
Apple's marketing is what gets me. There was the "I'm a Mac" ad that was, quite frankly, discriminatory. Middle-aged, fairly well-kempt guy who probably has a decent-paying office job versus the hip young teenager. "Hey, cmon, you don't wanna be old and, you know, not cool!" And most of it's just the older guy not being able to do things. Admittedly, there is a point- craptons of errors with PC's collectively- but they're generally not as bad as the commercials made them out to be. Most decent computers only crash or otherwise fuck up/get fucked up if you're doing something they're not designed to do, have a virus, or the like. Not to say there are never random/serious issues though.
And then there's Apple trapping, yes, trapping, Mac users into Apple-product-world, it seems. Only Apple products and nothing else work with Apple products, so you have to buy only from Apple to accessorize your Mac.
But above all else it's the people who own Macs that get to me. More than a few times I've heard a Mac user I know go on and on about how "Macs are so superior to PC's in every way like they don't get viruses because they're just that secure"- a totally bullshit point, by the way; windows alone account for approximately 800 MILLION machines, PC's without Windows a few more million/tens of millions on top of that. People make viruses to affect as many people as possible; Mac accounts for less than 15% of the computer market by a longshot, so no one wants to make a Mac virus that won't really hit anyone. I've heard them trash-talk PC's on a few occasions, talk about how there is no good thing about PC's at all, etc etc and then flash their shiny Mac at me and show me pretty colors. They generally act all superior and snobby towards me because I use a computer that most of the rest of the world uses, at least when computers come up.
So as computers, nothing against them. How Apple markets them, something against. How people think about themselves and their image when they have one, lots against.