I'm a nit-picky sort. Because I'm not fluent in all the lingo, I can get bogged down trying to describe visible differences or understand their optical causes, but they're certainly visible even in smaller prints. Being able to tell whether something is both detailed and sharp is a bit of a curse, because I'm often not capable of making things sharp enough
Printing on canvass makes a great cheat for obscuring the ultimate resolution just a bit - behind the texture of the canvass itself. If the picture looks good, people aren't going to critique the ultimate level of detail - likely still a lot higher than what they're used to looking at on their HDTV sets. Where I work there's a public gallery decorated with medium size color photographs on canvass (about 24"-30" wide). When you get close to them you can see detail break up just about in step with the weave of the fabric.
Is it too much to ask to be able to shoot like PJ and get detail like an 8x10 portraitist?
I hope you guys have huge success (and me too) and in a few years we're all debating whether 645 is enough, or 6x7 is needed to really get the job done.
For now, I say everyone should go for the D800 (or whatever it's called) as soon as it's announced and then post extensively about your experience with it so I can make a better informed decision...