Since when are IB processors delayed? MR just had a story how they have gone into mass production on schedule for a Q2 release.
I say wait if you can. It wouldn't be surprising if the next iMacs feature a new design (certainly not guaranteed but possible). Even if they don't, they should include USB 3.0 (and if you want your iMac to be compatible with devices in 4-5 years time, this may be important), SATA 3 SSDs, and of course newer GPUs. On top of that, maybe we will see the return of the 24" so if you are interested in that size over the 27" it might be best to wait.
When it comes to buying a computer today, I think it is foolish not to have USB 3.0 and an SSD. Right now, iMacs lack the first and are using 2-year-old technology when it comes to the second. March-June is not that far away.
5-8 months is not that far way
People honestly have a different perception on life, to me anything more than a month or two is to long. It's not about buying a computer just to get one, I only buy one when I need it.
Usb 3.0 is NOT going to do anything that I can't do with usb 2.0, firewire 800 or even eSata.
I will be buying a new 2011 base iMac upgrading from my 2010 base model. The biggest thing being that new I will have a true quad core cpu which will help me tremendously with converting and exporting hd files.
This 2011 base model iMac will easily last me 2 years before I even need to think about upgrading again.