Interesting: I've never tried doing a comparison like that.
What was the subject in the photos? As BJ says, it's more of a problem with landscapes where every last bit of detail counts.
The problem I have with large prints (12"x18") from my D1 is the natural human reaction to examine them up close. They look really good at a proper viewing distance, but they don't stand up to the close examination. There's no pixelization - they look more like a really finely detailed watercolour.