In many cases, buying a PCI WiFi adapter would actually be a better choice. That being said, using a USB WiFi adapter isn't for everybody. This means that you might not even have to buy a new adapter for your Hackintosh if you already own a USB WiFi adapter, there's a decent chance that it'll work in Mac OS X. It's not a big price difference, but it's still something worth considering. Sometimes, you can even find USB adapters on sale for half that price. Mini-ITX motherboards are even worse most of them only feature a single PCI slot, making a USB WiFi adapter all the more important. Micro-ATX motherboards usually only come with 2-3 slots.
You may not want to waste an extra slot on your WiFi adapter if you plan on connecting a lot of PCI devices, such as graphics cards, sound cards, Firewire cards, RAID cards, TV tuner cards, or so on. USB adapters don't take up an extra PCI slot. Most motherboards have a relatively limited number of PCI slots.
