Hmm, an actual question from Evan_Mann. This would be better suited in Voting Forum, I think.
I depends on the deck I'm playing with, generally. If I'm playing Sligh or something of the like, one land should be enough. If I'm playing some big combo deck or something that doesn't usually support itself on 1-2 lands, I'd mulligan.
Well, back in the day when I used to play, 1 land was almost surely a mulligan, unless I had a key card for a combo in my hand or a creature I could drop first turn.
Minus quick supplimental mana (land grant, moxen, etc.) you almost always mulligan. Even with a hand full of 1 drops, you want 2 lands so you can drop 2 1CC creatures on turn turn and swarm like sligh and stompy are supposed to.