I'd be more concerned about the new price tag of the GF3. I think you can buy a GF3 right after the release of a GF3 Ultra and a GF3 Ultra right after the release of the GF4 for less money than the GF3 Ultra would cost you on debut. So, if there are no games or applications you are likely to run that will not yield any perceivable difference in that span, it is more economical to go the aforementioned route.
But, heck, I want the biggest baddest video card money can afford; even though it's been about a year since a 3D game was run on my system.