Nod. If I had a nickel for every web app I've thought of and could have executed on but didn't, only to see others take the same idea and launch...I might have a buck fifty.

I should qualify that when I say the Amazon feature is "obvious", it's only from my perspective as a user. I would want a site-independent wishlist for the simple reason that I wouldn't want to manage wishlists on multiple sites. Only now, however, is it clear to me what the business incentive is for that.