I say, if you have the opportunity to send your laptop back and get the new one, you might as well. What is there to loose, other than a few days without it?
I bought myself a Powerbook G4 12'' about 3 weeks ago, so there's no returning it for me. While the update is nice, it doesn't do anything that is really groundbreaking. The speed is ok, but for what I'm using my PB for (notetaking, paper writing, web surfing), it would be barely noticable. I don't play games on it (I have a killer PC for that purpose), so the extra video RAM is of little importance. The only thing I'm a bit miffed about is the built in Airport Extreme which I had to pay $89+tax to get. That's life I suppose, there's always something new.