[obituary_latte]

Probably as enforceable as any other EULA. Windows surely has similar language. I'd guess that somewhere buried deep in the agreements, or somewhere, it says they can audit your usage somehow. Does it ever happen? I'd be curious to know.

[naikrovek]

Windows doesn’t have similar language. Not directly, anyway. Depending on the edition of Windows you purchase and how your overall license agreement works, you get anywhere from zero to ten VM licenses per paid Windows license.

I’m omitting a few details for brevity (MS licensing is nuts when you get into the weeds).