If it's a hobby machine go for it. They can be a lot of fun and a good way to learn more about OS X, but if it is a work machine I wouldn't recommend it. Things break all the time, updates will Bork your system. Sometimes the App Store won't work. Power use issues, it's just a lot of work.
If it's a work machine I recommend buying a base Mac mini, then adding an ssd as a second drive and maxing the ram yourself. You will get a screaming fast machine for anything that isn't too graphics intensive like hardcore gaming. And it will probably cost you about the same or less as building your own hackintosh.
Just this, great for a hobby machine, but honestly it's next to impossible to use as something you have to relay on.
For me, it's just about updates and iMessage. I use iMessage a lot, and their security means it doesn't work on a hackintosh. Next are the updates. The issue here, is that graphics doesn't work, or the machine doesn't boot, etc. All fixable, but often you have to debug it once or twice.
Problem I had with the Mac Mini was I bought mine as the basic model, and its so slow to use, the hackintosh is better. However, nothing works as well as my MacBook for actual work.
Right now, personally, I'm waiting for the 5k iMac and when it can be used as an external monitor. I upgrade my computer every couple years, but my old Apple Cinema Display is 7 years old now, so I really need an iMac to be usable as a 2nd display. Hopefully september will bring that update.
Yeah could do, but the problems with the hackintosh are a pain. I honestly can't wait to upgrade. My current CPU is the intel 3770k and the 4.0ghz iMac processor is around 30% faster at max usage.
I've moved most gaming to consoles, just not super interested in PC gaming and the iMac can still do most of it.
If Apple bring out a Mac Pro though with a gaming performance GPU I might consider that too, but thats never going to happen any time soon, lol.
Also finally I love the glassy reflective screens. Just so used to them these days and using anything but is just odd to me.
Well to get it working requires faking a product hardware I'd that is not in use. Issues with that or mistakes can cause you to be blocked from iMessage on all devices. So for me, not a hassle I want to put up with.
Strange how most of the comments don't address the actual question- what off the shelf PC makes a good hackintosh?
The only off-the-shelf PC I've seen used recently is a Gigabyte Brix (Gigabyte does make motherboards too but this is a complete computer).
Dell, etc. use their own BIOSes and while they may be compatible with hackintoshing, not many people are putting much effort into making them compatible. You may not be able to turn off certain instructions from the BIOS that cause crashes.
Avoid AMD processors and AMD/ATI graphics chipsets; not as much effort has been put into making them compatible.
One other detail- your legal OS X still has licensing terms that basically say if the box you install it on doesn't have an Apple on it, you're violating them.
I would really advise agains even trying, unless you are simply bored. I created a system with exact parts recommended by tonymacx86 and it took days to get everything up and running. Even then basic stuff kept braking like sound. Speed stepping didn't work at all so I abandoned that ship...
Been running Hackintosh for 5 years and have always used Gigabyte Motherboards. They generally work out of the box using tonymacx86 installation tools including upgrades.
Get an Nvidia Card (Any current model will work) if you want to avoid installation issues and get the best performance (Nvidia have native drivers for OS X) and make sure to enable TRIM on SSD's.
Back in college days, I made my dell laptop a hackintosh, at that time ati was not supported by osx, so it was very troublesome to install - patching dsdt, kexts and all. It broke when I updated to Lion and I stopped and installed Arch Linux. I used to check http://www.insanelymac.com forum, http://wiki.osx86project.org, and, http://www.tonymacx86.com a lot. There you will find most of the resources you need.
You might find these links useful in finding a compatible pc if you don't want to do diy:
There are few OEM that are actually Plug'n'Play, and even with those, you will most likely have problems with OS X updates.
If I were you, I'd really go with DIY, fewer problems and you will gain experience.
johng linked to tonymacx86 which is a useful resource, although I don't really like MultiBeast since it's not actually the All-In-One solution it's supposed to be.
Depending on why exactly you want a Hackintosh you might want to check out Elementary OS [1]. It's a Linux distro that has the same sort of feel as Mac OS (and it's free).
If you're looking to do development for Apple products though you're probably better off just buying a Mac.
I would never understand advising getting a derivative of Ubuntu for the sake of the UI. But I agree that if the OP wants to use Apple's environment he should consider buying their product. I personally would rather use a Linux/BSD system.
There are optimized parts for a hackintosh, which is why it is best to DIY.
As far as buying, the retailers will skimp on areas that are negligible or ignored by the consumer, e.g. motherboard, RAM, PSU. This makes it difficult to work with compatibility & OSX from a straight buy perspective versus choosing each optimized part in a custom build.
As a warning, you might run into issues with seamless integration that is normally experienced with Apple products via MBP/iPhone/iPad. The 'ecosystem' doesn't like Hackintosh :D
I built a hackintosh a few months ago because I really prefer OSX for development compared to working in Windows or Linux. I spent around $700ish on desktop parts, (i7 cpu, 16gb ram, no video card but using the intel HD default graphics) I've been using it as my every day machine and it runs great. Including running windows VM's in virtualbox etc. Only thing that doesn't really work is the USB ports, which in the grand scheme of things is kind of minor.
Have you considered virtualization? Before adopting OSX, I went the virtualization route myself 4 years ago. I know it works on vmware (at least for me back then with vmw player running on Dell Linux laptop).
It probably depends on your requirements. YMMV
If you're going through this to save a few hundreds, get a mba refurbished.
I have Lion, Mountain Lion, Mavericks, and Yosemite running in VMWare Workstation. They work well enough to do web testing in Safari, but the video performance has been too slow to do much else, so I don't use them for anything too serious.
If it's a work machine I recommend buying a base Mac mini, then adding an ssd as a second drive and maxing the ram yourself. You will get a screaming fast machine for anything that isn't too graphics intensive like hardcore gaming. And it will probably cost you about the same or less as building your own hackintosh.