I just came across this short paper on the usability of YouTube that I thought was interesting given the recent discussion here and on Stephen Few's blog. The authors point out that YouTube is a hugely successful site despite sporting an interface design that apparently doesn't respect many conventional usability heuristics. By considering what users enjoy about the site, and what keeps them coming back, they suggest that these traditional evaluation methods may need to be redefined; among other things, "engagement" and "playfulness," two terms we've been throwing around here lately, are becoming increasingly important.
While I won't argue that YouTube serves the same purpose as information visualization (particularly if its "apparently bad design" is intentional, as the paper suggests), what I find most poignant about this article is how it identifies the "new" Web 2.0-enabled user, a digital native that grew up with the web, as having a heightened literacy for the internet and its technologies. This new user interacts with information differently and more fluently than users of the past, so the design of interfaces for them should reflect this -- a sentiment that certainly applies to information visualization design as well.