Since the AppleTV doesn't show up in iTunes anymore - I'm in the process of doing a restore which will download the latest software and install it - I'll let you know if it's still 4.0 after
Quick note:
AppleTV - Hardware Version 1:
1.0 - Original Front Row Interface
2.0 - Rentals (Take Two)
3.0 - Minor Changes (but still 3.0)
AppleTV - Hardware Version 2:
4.0 - Netflix, $1 Rentals (so this may be iOS 4.1 even though it's called 4.0 - seems odd not to call it 4.1 or 4.2 though)