Intel will be releasing the mobile and ultra-mobile Haswell chips first (seems odd but true) in early 2013 and I haven't seen any dates on when they will release their desktop chips so I wouldn't have a problem buying Ivy Bridge in the next few months. Besides, the main improvement for Haswell seems to be power consumption, which is less relevant for a desktop like the iMac.
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I have been waiting for a new iMac for months to *replace* my hackintosh, which I've been using as my day-to-day machine for about 3 years. It is amazing that you can get OS X working on (some) standard PC hardware but it's a hassle that I want to get away from. The sleep function on my computer doesn't work reliably, it hangs about 1/2 the time, so that's miserable. Also updating to a point release of the OS (e.g. Mountain Lion) takes a solid 1-2 days of work--reading message boards, reinstalling stuff, etc. Also, my cable internet provider started doing something weird the other week causing my hackintosh to drop its network connection every few minutes because of a driver issue, and futzing with the drivers on a hackintosh is NO fun.