Yea I wouldn't recommend doing anything other than hopping between buildings or vehicles when it gets down to -40 (same in both C and F, which I think is neat)
-10C is 14F, which I agree is a pretty nice day if you're properly outfitted.
You can actually do stuff in -40C, just wear a lot of clothes and don't expect your digital camera to last very long when you are trying to take picture of carved ice sculptures and ice bars, etc...
Honestly, the coldest winters I spent were in Southern China, even though it was 5 to 10C out, no indoor heating really sucks and will beat you down quickly.
-10C is 14F, which I agree is a pretty nice day if you're properly outfitted.