It's a great list, but could use some clarification on some of the items as to which way best practice lies. I would place myself somewhere in the early- to mid-intermediate level and some of them I wasn't sure on. For example:

Is write-warning or write-error used for problem messages?

Are errors signaled with write-error?

Is the implication in the first question that those two shouldn't be used for problem messages? Or that you should stick to write-warning for problems and write-error for errors?

And:

Are named parameters used instead of positional parameters?

I know positional is ideal when the logic follows that way, ex. the password parameter right after the user parameter, but is the implication here that any named parameters are bad? I tend to use a mix of both.

Also, I'm one of those guys who sticks Read-Host in a while loop. I also put Write-Host in while loops to generate menus, the options of which trigger those Read-Host loops to gather parameters. The reason being is because if I didn't bundle a menu script with my module, nobody would use it. :|