I once saw some interesting behavior on a Windows 95 machine - my brother printed a drawing for a convention to a file. The printer was a HP LaserJet with plug in module that enabled Postscript. He named the file "con" and when he hit OK on the print dialog the entire screen buffer (over the windowing interface) started filling with Postscript.

We're encountered this issue when dealing with ETF tickers. We use Linux but a 3rd-party redistributor was on Windows; the reports we created had file names in the form <TICKER>.pdf and, what would you know, PRN.pdf caused all sorts of trouble for them...

"finally the behavior of the window filesystem is so incredibly broken that well they should really fix it I guess."

Ha. Just allow "prn", I'm sure that won't have any side effects.

There's countless batch files that rely on NUL (including with extensions, usually because some other batch file is appending the extension). Most of the other ones could probably be safely removed, but it would still run contrary to Microsoft's policy of not breaking backwards compatibility unless absolutely necessary.