In my current campaign (5 sessions in), all the PCs started as lvl1 commoners. We played 3 sessions like that and they became upgraded their commoner level to a class level of their choosing.
It was very fun, albeit quite disconcerting for the players at first. It was very challenging for them to do anything, so rather than rely on the dice, they really took up the roleplaying reins and got involved in the locale.
It really helped establish what I think of as the first-level feel. They had to be careful what situations they created or got caught up in, because they couldn't fall back on combat ability. They used their limited skills to the best of their ability, but they didn't have much to work with.
Now that they've got a class level, it really feels like they advanced by working hard and getting better, not by inhaling magical xp dust.