He used to be pretty humble in the first dozen episodes, but he's slowly gotten a big head and turned into a dick. At least from my perspective.
I don't recommend his app any longer, instead, I suggest people use one of it's competitors, Read It Later.
Again, the podcast isn't so much about building apps as it is a soapbox for him to complain about other applications and other developers. While he does discuss some of the aspects of Instapaper, he may as well have called the podcast something else. If you're expecting developer oriented discussion there are better podcasts to listen to.
If you're going to spend time listening to a 5by5 podcast, I suggest two that are much better. Hypercritical with John Siracusa. John at least knows how to complain while being constructive, unlike Marco. The second would be The Incomparable, on a totally different topic but very worthwhile.
As as example of marco being an ass. Just listen to any of the podcasts from 10-onward. Also, listen especially to the programming episodes where he tries to argue against Siracusa but instead sounds like a whiny brat.
edit: Keep on down voting people. Seriously. It's called an opinion. If you don't like it, too bad. But it helps people make a valid attempt at determining whether they want to listen to something, or read something, otherwise spending their time with something. Make your own opinion of the podcast and Marco. But down voting simply because my opinion is different than yours is just stupid.