[bigd]

Writing underwater, in space and at non standard angles. Pencils could not care less about gravity or lack of air, and have a wide temperature range of operation. I've no proof on this, but my guess will be something like -150:600 ± 50C.

[lomnakkus]

Pencils can be actively dangerous in zero gravity: See http://en.wikipedia.org/wiki/Writing_in_space