The answer to both questions is "not much". It's certainly enough to light several fires in good conditions, but I wouldn't rely upon it to dry out my tinder before lighting it or as any sort of long-term light source on its own.

My most recent tool maintenance exercise found that my peanut and split pea lighters had not lost a measurable amount of fuel in three months. Just make sure that you check the o-rings and replace them at appropriate intervals.