Seth can't quite be taken at face value. His positive mental attitude is on overdrive. His happy meter starts at 11. His eyeglasses are shaded so rosy that he can't see anything in 12% of the visible spectrum.
Still, much of what Seth says is correct. He's certainly done quite well with his "do happy things and happy things will happen to you" PLUR appoach to life.
But even then, what Seth practices and what he preaches aren't quite in accord. These day's he's mainly cranking out volume after volume of feel-good books that are so short they could almost be magazine articles.
Still, I often find myself recommending Seth's books to people. Why? Because most of that he says is correct, even if it is saccharine sweet.
To really succeed, you have to work on projects that you enjoy. But, you can make millions of dollars in bottom line profits without doing that. And maybe that's not such a bad compromise for most people?
Let's take the three U's you mentioned:
Useful -- That depends what you mean by "useful", Senator. Plenty of sites are completely useless at anything but wasting time -- and some of those sites are very popular.
Unique -- HubPages isn't unique, but it's beating Seth's Squidoo by quite a good margin.
Updated -- This is the one I have the most problem with. "Updated" is critically important in some niches. In other niches it's irrelevant. Most niches fall somewhere in between. It's best to be very careful in applying Seth's platitudes to your niche.