So today I see this question poised on linkedin.com: "Which site has the best navigation design on the web?"
To that I respond:
In what capacity? It's easy to say that Amazon has some of the most robust commerce user-interface (UI) deployments online but it's also easy to say that Facebook does too from a social capacity (though hated by many). Facebook having recently hired Matthew Papakipos former director of engineering at Google will increase their attention to UI and data development as well. I think that hiring someone that not only understands UI but how it reacts in an a full operational environment (i.e. Google Chrome) was a really smart move on their part.
Then you can also make the case for 'design over substance' when it comes to navigation. Advertising agency Leo Burnett - has a interesting "exploratory" navigation, it's hardly useful (IMHO) but it's very cool. That being said, given your demo it might be the right approach. I would say that the tween' and teen markets are the most sophisticated as far as excepting UI learning curves. There's an natural tendency for game-makers to design increasing levels of complexity in all facets of game play. I see this as an almost intuitive understanding from these age groups. While the rest of us struggle to find the old tools in CS5 that we can't live without, the rest of the young world is finding it exactly where they thought it should be.
Back on point -- So is your market commerce based, app based, social based or simply a website intended to be added to an already preexisting marketing mix? These are important questions that need to be answered long before informational architecture and wire frames are even created.
The rule of thumb for most is one click with a high "K.I.S.S." (keep it simple stupid) factor. It depends on the kind of site you intend it to be – quick hit (Twitter) or long term profile based 'i cannot live without checking this site 10 times a day' (Facebook, YouTube, etc..) For sites that intend to increase dwell time such as Facebook, Flickr, YouTube (and in some instances amazon) the time-sink can be constructed by becoming progressively more complex the deeper you fall into the website. Much like game play previously discuss, you start with the standard login and thirty minutes later you've loaded five application on your profile and you're being attacked by zombies.
Then there's tier-based navigational structures such as ESPN and CNN. The home page is a sea of choices and possible interests, refining itself the further your deep linking takes you until, more often than not, you fall into a pretty specific article. Once you've captured the users attention at the basement of content they then eloquently advocate you share the data in one of a hundred ways.
Lastly, I think there's something to be said for sites such as most Wordpress layout (such as this website). Simple, standard horizontal or left/right hand vertical navigation is constantly still being adopted. Like it or not there's a reason why it's weather the storms. Will yours?