ITP is a joke coming from a CS background. It's good for internet fameball self-promoter types and people from an design/art background.
Disclaimer: I come from a CS background (Stanford), but work at a company (Foursquare) where several of the non-engineering founders/early-employees come from ITP, but the engineering team is entirely non-ITP. Also, two of my closest friends have been in ITP. Other than that, I have never been personally affiliated with ITP.
The vibe I get from ITP is definitely a mixed bag of technology and art school. Coming from my background, it feels much closer to an art school than to a CS school. I have no doubt that I would be immensely frustrated in such an environment. Consequently, I've never seriously considered going there, despite the insistence of several close friends. I recognize that ITP is not for me: my technical skills would likely not improve much as a result of going to ITP, and the art-school-vibe would be both unpleasant and frustrating for me.
That said, I can see how certain people could benefit a lot from ITP. If you're an art-inclined individual that wants to get in touch with your tech side, at least enough to be able to build your own prototype without having to rely on someone else. (E.g., get rid of the "I've got a great idea and I'm looking for a technical co-founder" problem... surely everyone on HN can get behind that.) Or if you're a tech-inclined individual and want to get in touch with your art side, to explore how people interact with technology and how even simple technology can drastically change everyday behavior. I think both of these people could benefit from ITP.
The biggest startup successes recently (Facebook, Twitter, Groupon) didn't start with any kind of technological edge. They were a simple PHP website, a basic Rails stack, or practically a static HTML site. Of course, SIGNIFICANT and SOPHISTICATED engineering effort has gone into making these sites scale to their current success, but they proved their worth and achieved traction with little engineering effort. Generally, they distinguish themselves from the pack via their softer side, by building communities and human value through good product design rather than technical prowess. The initial version of Foursquare was a tangled mess of PHP code that was clearly written by someone who know just barely enough to get the job done. You could read the code and cry. But it was enough to get them to tens of thousands of users and millions in funding.
So yes, there are many reasons not to go to ITP. But even a technical person who aspires to be a startup founder could find many reasons to go.