I've known about SketchUp's Project Spectrum for a few years now, when Tom Wyman first spoke with me about his work with the Boulder Autism Society. Turns out that this application which was designed for architects somehow got a foothold with some autistic kids, who were able to communicate complex designs on the computer, even if they couldn't express their ideas verbally. Seems SketchUp mimics the way an autistic mind works, which was confirmed to me once by an overjoyed book customer who was thrilled to have discovered SketchUp.
And having a mildly autistic son myself (he's only 7), I've seen firsthand how SketchUp can bring out some inner creativity which might have otherwise been hard to tap. For a kid who has issues focusing, he can sit and design different houses for 30 minutes, without any fidgeting or redirecting.
Newsweek now has a piece on the SketchUp-autism relationship: http://www.newsweek.com/id/179952