It is not security through obscurity. It works even when the attacker knows I use a passphrase and has a copy of my dictionary. It's about the same security as a random 8 character password with lower and upper case, numbers and choice of 10 symbols.
Maybe that's no longer secure enough; I don't know how fast password crackers are now. So use "shuf -n 5" instead.
It doesn't work when the attacker knows you use this scheme, your username and the site's domain. There's no secret in that scheme, therefore it's pretty much the exact definition of security through obscurity. Add a password to it, though, and you pretty much have SuperGenPass.
I think you replied to the wrong person here. I'm saying that the passphrase does not rely on security through obscurity. venomsnake's scheme does, though it appears he meant it to be exactly that (ie. an example).
Yeah, that was weird. You are correct in that comment, I posted the entropy equivalents in another comment in this thread (using 5 words is pretty secure).
Maybe that's no longer secure enough; I don't know how fast password crackers are now. So use "shuf -n 5" instead.