Al over at Beyond the Black Gate asks an interesting question about what is powerful in your D&D campaign.
My general rule of thumb was inspired partly by the D&D level titles goes like this.
1st is the initial apprentice level, some body who is newly trained.
3rd is when you are considered a full member of your profession.
9th i.e. name level is when you are considered by most to be capable to handle being a leader of your profession.
16th level i.e. Mage level is consider highly skilled grandmaster level.
18th level i.e. ArchMage means you are one of the top 1% in that profession.
When I played AD&D I went by the populace has level style. In my current S&W/MW campaign I still do that to some extent but because now I have the NPC classes, thank Jeff Rients, they are "leveled" but are considered 0-level for combat. Leveled individuals have the same ratio to the general populace as nobility did in western europe. If you just pick a random person off of the street they will be zero level but if you look at who adventurers normally associate with then the number of leveled people they run into goes up considerably. (i.e. nobles hanging with other nobles).
I may refine the NPC classes further in regardless to fighting classes to better represent society. It is important that I approach this the right way in Swords & Wizardry as the fighter's ability to get 1 attack per level against less than 1 hd creatures is an important class feature. If I was using AD&D, with it's multiple attack per round at higher levels, it wouldn't be as much of an issue.