How to delete all the files in a folder except read-only files?

Question

I would like to delete all the files and subfolders from a folder except read-only files.

How to do it using powershell?

Answer 1

For reference, this is a bit easier in V3:

Get-ChildItem -Attributes !r | Remove-Item -Recurse -Force -WhatIf

or the short (alias) version:

dir -at !r | ri -r -f -wh