It seems like we should have almost everyone at the same level, and have that level be available for the asking, and have that level be mostly nondestructive, i.e. every action is reversible, although some might be a pain in the neck to reverse. So it might look like this:
1. Newcomers -- can do everything except a small handful of actions, actions which are "pretty serious" like temporarily blocking an ip or deleting a page.
2. "sysop" or better terminology might be "community member" -- can do some extra things like nondestructive delete, temporary ip blocking (which should affect only newcomers, not other "community members"). The important _wiki_ ideal here is that community members shouldn't be able to do anything extra "in a content fight" if you see what I mean. We'll all the same, newcomers and community members, when it comes to the content -- one "check" here is that anyone can become a community member just by asking... it shouldn't be all that special, and certainly not an exclusive "club".
3. "developers" -- the main extra thing that developers should have access to would be "raw" stuff that's pretty technologically "dangerous" if you don't know what you're doing. I.E., ability to enter arbitrary SQL select statements, even ones that might be really slow. This extra power should only be used for development purposes, and not "in a content fight".
4. "sysop" -- of which there might only be 1, me, or a very small number. The sysop can do things that might be legally necessary, like immediately and totally deleting copyright violations, or things that might be necessary to fight a serious troll attack, like semi-permanently banning whole ranges of ip numbers. For most things of this nature, there's probably no need to worry about it in advance. Anyhow, "sysop" powers must never be used "in a content fight". This would be like Superman cheating at poker by looking through the cards. :-)
--Jimbo