Well, no one will know for certain other than Apple themselves when the new iMacs will be out. But it does seem to make sense that the iMacs will be updated soon with the new processors from Intel already rolling out to consumers.

I guess if you got a good deal on the 2nd hand unit and don't mind the fancier new units, go ahead.

Although i wont disagree that there is a new imac in the pipeline, it is highly unlikely that it would be revolutionary. In fact, my favourite Imac of all time is Imac G4 "iLamp" I find it incredibly difficult to believe that quadcore to come into imac and eat into Mac Pro's market. It doesn't make sense although it can be true. All the other stuff like sd slot, new mouse and remote aren't that significant. Im sure there are people are NOT using the mighty mouse now and trust me, it probably make no difference to their apple experience anyway. If you can hold, then just hold on, rumours is that it is soon but it is pretty much spontaneous.

Rumours exist because of the product life cycle is almost up. That estimation is based on the time it took Apple to change previous versions.

Hope that helps. Cheers