The take home message of each poster: "Think Different" juxtaposed with someone who changed the world through their passion and their achievements - I think that's really powerful. It's no wonder that originally, Apple sent them out as complete packages of posters to schools and educators all over the country.
The campaign was a huge success and you can read more about it here, at the Low End Mac blog. Now, more than a decade later, the series in both sizes, 11x17" and 24x36" are highly sought after and have become major collector's items. Just one like the Jim Henson poster here is selling for at least $200+ on eBay and other sites.
If you're interested in making the investment, I've read that they are only going to grow in value. One site where you can readily get them is here, at the Missing Bite (overpriced in my opinion, but consistently available right now). I'd recommend purusing eBay and craigslist, however, you should be cautioned that there are many fakes out there. eBay has a great article that details what may constitute a fradulent "Think Different" poster so be sure to consult it before buying.
Even if you can't afford one of these posters now (aka you're like me) - take a second, be inspired, and watch 59 seconds of the Apple "Think Different" commerical below.