I run a 120mm Reba Race on mine and the only other blizzard i've seen had 120's too.
Tried it for a few weeks as 100mm and the front end felt very low, kick you over the bars low on some stuff! Adjusted the forks to 120mm and it's a much better bike for it. Climbing isn't all that different but descending or twisty singletrack is much better. It's easier to pop the front wheel up to get out of ruts and you don't feel like you're going over the bars should you need to lift the rear wheel.
As for the warranty… it's not like i'm doing 30ft gap jumps on it with a 140mm triples and they say the frames are seriously strong so i figured another 20mm isn't going to kill it.