I'd be happy to say more (why, data, etc.) on anything in particular. The post was already getting a bit long, which is why I left it at that. There is some why in there already though.
"Use directories instead of subdomains."
This is why choosing one main domain for you website (either www.example.com or example.com) and 301 redirecting all requests from the one not chosen to the chosen one is recommended.
The point is: don't automatically just shove everything in subdirectories; think about if you want your subdomains to have independent PR or not - it might make sense in certain situations.