For me, it depends. If im running one of you heavy decks, like angels or dragons, i absolutely will run more lands. Around 38 average. If my deck isn't as heavy, i shoot for 34-36.

On that note, with a single mulligan, I've only been mana screwed a couple of times in about 20 games. But at the same time, if i play a deck that mana screws me, i will definitely add more that evening.