Oh yeah . . . I forgot to mention (probably unnecessary, since most folks' comments I've read here seem pretty intuitive, but I'm way too OCD), the aspect of creativeness didn't just apply to art geeks like me . . . all sorts of engineers and architects as well. It's one of those toys that let boys and girls use their creativity and see not only how something looks, but also see the real-life implications of their planned structure using only the materials at hand.
After I saw Airport 77, I just HAD to build a 747, and 'fly' it down one of my strings . . . but I had to do it outside the house, and run the string from my little tree fort. Too big for inside. I'm sure you can imagine how many times I had to sift through the grass looking for pieces of Lego after the little cable-car-ish track wheels went 'SPROOING' off my 3 ft long plane and was obliterated on impact before I finally got a safe landing (the landing itself took a few, too). Spending ten seconds playing and an hour looking for all your parts can really focus a person.