Most of the points here are "don't do it, but if you do it's not a problem".
It should be renamed with "Be careful about this"
I don't see sufficient justification for "Don't use serial"--the some weird behaviors links to a 404 page.
The "Don't use varchar(n) by default" reasoning is similarly weak.
This post doesn't doesn't give enough detail reasoning to be self-evident, and other than the quality of formatting could be a collection of anyone's blog posts. Some recommendations seem to be solid, but mixed with the arbitrary ones loses some of its recommendation strength.