T. Foster said:
IMO it should take surviving through around 4 sessions for a character to gain 2nd level, and this should feel like a significant accomplishment to the player (especially since he's likely had a false start or two (or twenty) of characters who didn't make it, including some who may have come tantalizingly close). I don't like the idea of an assumed rate of progression and that implies that all a player has to do is show up consistently and he'll eventually get a medium/high level character. I prefer the notion that many (casual or mediocre) players will never get a character to 2nd level, even more will never get a character above 3rd or 4th level, and only the best (or luckiest, or, most likely both) players will ever have high-level characters achieved through actual play. To me, having a character of 7th-8th level should be a sign that 1) you've been playing this character regularly for a year or more (assuming weekly to bi-weekly play), and 2) you're really good -- at tactics, problem-solving, negotiation, effective teamwork, outside-the-box thinking, risk assessment (knowing when to run away), etc.