The biggest loss would be in giving up the screen real estate (1024x768 on the iMac, instead of 1280x1024) and the nice 19-inch Trinitron monitor. OTOH, I would be able to move the TV and VCR to where the monitor sits now, next to the iMac, and both reduce some cabling clutter and make room for the ham station.
It does feel strange to be thinking about moving out a Unix box in favor of a Mac. Just goes to show how right Apple has gotten OS X.