Omo on doujinshi + related nonsense

Omo made a nice post about what doujinshi is.
It has (nearly) just about everything I can think of regarding doujin, and it’ll probably be really useful for guys who are new to doujin, since there are probably a lot of guys who have only just learnt about doujin due to stuff like Touhou or Higurashi.
Also not directly related to Omo’s post but there appear to be many questions around why ZUN wants to limit touhou doujin works from commericial distribution.
Scenario of a Touhou doujin anime being commercialized:
1) ZUN rejects offers from anime studios to make official Touhou anime
2) Doujin anime gets made and sold through commercial distribution
3) Studios go crazy and start dancing naked while shouting Sanae-san
4) Totally awesome ninjas get hired by studios to kill ZUN
5) Studios make their own “doujin” anime for commercial distribution
In all cases derivative doujin works are allowed because they are fan works, but if they enter full commercial distribution then they can’t really be treated as doujin anymore.
This is the same for working on anything that’s a derivative work based on someone else’s work.