> I also imagine this will be a great way for a lot more people than the 0.15 to 0.17% of the population that actually has Delayed Sleep Phase Disorder to rationalize their lack of willpower.

Yep. Unless you've been professionally diagnosed, just pointing to a Wikipedia page and saying "I have that!" as an excuse for your behaviour is not the right thing to do. The same thing happened with Asperger Syndrome; it became the excuse du jour for dickish behaviour. "Oh, I'm not anti-social, I have Aspergers." No, actually, you're just a dick.

Using "I have this-or-that disorder" as an excuse (unless you have been professionally diagnosed) is just that: an excuse. It also belittles those who actually do have the disorder, which could be an even worse side effect.