OK, here is something else that might matter to you. If you do sell and un-register and then attempt to file a rebate for the G4 purchase, be advised:

You need to provide all the info in the rebate PLUS you need to include something that proves you owned G3/3.5 when you purchased G4. Their proofing check of your rebate info only checks to see if the older model IS NOW registered in your name, not that it WAS ever registered to you. And they probably will see that it's registered to whomever you sold it to. And they'll then reject your rebate.

They were nice about it when I sent them a copy of the email from them to me acknowledging my un-registration. That proved I owned G3 and G4 both at the time I sent in the rebate.

I HATE FRICKIN' REBATES. I consider them to be very close to an attempt to defraud.