Carmack's a legend - he's done good things (which I can't talk about) for the WebGL community too, ask Tojiro next time you visit a conference.
Weird Quake/Doom crossover: Doom had 'rocket jumps' (pushing yourself further off a cliff via smashing a rocket into the wall) - one was required for the E3 secret level.
Doom also had accidental wall riding but only when you were headed north. :^)
It's due to the 'sliding' check on walls, if the player is moving fast enough, the movement path is divided in half and each is checked for obstacles...but if the obstacle happens to be in both segments of the path, you're slid twice.
And the reason the bug only happened when you're moving north and east is due to...another bug, the check is done only if your movement is greater than X or Y, not if it's less than negative X or Y.
