Are you referring to specific bans or a general case?
In general I've been called pretty soft on first time bans, but I believe a week or two is long enough for someone to consider whether they want to return and abide by the rules or not. Subsequent violations are treated much more much harshlu, and sock puppetry or ban evasion will make me a very sad panda.
That being said, that's just MY philosophy. I'm the primary mod here now so my philosophy is probably most relevant (and I'll note bans in this thread), but I can't speak for anyone but myself.