Sorted by severity:

Crime: Trolling
Trolling is acting like an idiot for the pursuit of hilarity, or otherwise screwing with people in a manner that does not ruin the game.
Punishment: Nothing
Yep, that's right, nothing will happen to regular trolls.

Crime: Role-Quitting
This one is obvious. This is for all those people who ruin games and setups by leaving just after seeing their role card. Example: "DOCTOR? Fuck this, I'm out."
Punishment: Shame
Role ragequitters are bad people.

Crime: Griefing
Griefing is similar to trolling, but actually results in the game being ruined. This is trolling taken too far.
Punishment: Watch List
If multiple people can confirm a griefer, they will be put on the watch list, which will alert everyone in-game that the player is a griefer.

Crime: Cheating
Cheating is using methods unintended by the game (such as abusing Skype) to gain an unfair advantage over other players.
Punishment: Watch List or KickVote List
If multiple people can confirm a cheater, they will be put on the watch list. If further infractions occur (and a moderator can confirm it), they will be put on the KickVote List (which initiates a kickvote to remove the player upon the start of the game).

Crime: Game-Throwing
This is intentionally playing to lose. An example of this is a Mafioso giving out the names of his fellow Mafia to the town during his trial.
Punishment: KickVote List
If multiple people, including a moderator, can confirm a game-thrower, they will be put on the KickVote List.

Crime: Abuse
Abuse is abusing donor or (more seriously) moderator abilities. This includes kicking people at random, cheating with the mod message system, etc.
Punishment: Demotion / Watch List or KickVote List
If many people (especially if including a moderator), can confirm a privilege abuser, the punishment will vary by situation. Donors can lose their abilities with a demotion in extreme cases. Moderators will lose their abilities, and be placed on the Watch List or KickVote List depending on severity.

Crime: Hacking
Hacking is obvious: getting donor codes or moderator abilities, modifying bank files, mining players' roles, etc. are all examples of this.
Punishment: Point Ban and/or KickVote List or Ban List
If multiple people, preferably including a moderator, can confirm a hacker, they will be punished. The punishment depends on the type of hacking; modifying the bank will result in a point ban (permanently set to 0 points and no achievements), while hacking moderator abilities would be enough to be on the ban list if multiple existing moderators can confirm (permanently removed from all Mafia games).

Crime: Donor Code Leaking
The rest of these crimes attack the spirit of the game and its gameplay; this attacks my money directly. As such, I (and quite a few donors) consider it to be the worst of the bunch. Donor code leaking is exactly what it says on the tin: intentionally telling people (aside from other donors) what your donor code is.
Punishment: Demotion / KickVote List or Ban List
If multiple people, including a moderator (preferably multiple moderators), can confirm a leaker, their donor code will be expunged and they will be banned from further games of Mafia on the Ban List or put on the KickVote List, depending on how much they donated to get the code in the first place ($1 donors beware).

Please note, in any case where a punishment requires a moderator or admin but lacks such endorsement, sufficient evidence will still award the Watch List punishment.

A first offense Watch List or KickVote List will last for at least 1 whole week, except in some situations where I will enact a time extension (usually double the original time). After the time is up, they will be demoted by one list and given double time there, so someone on the KickVote List will drop to the Watch List for 2 whole weeks (ignoring the original time extension, if any). Ban List sentences are 2 weeks by default, though in some cases I might give only 1 week or (in very rare cases) even an infinite sentence, i.e. a permanent ban.

Punishments for repeat offenses are doubled each time. For example, if someone makes the KickVote List once, which completely expires after 3 weeks, then gets on the Watch List for a different crime, he will be there for 2 weeks instead of 1. If that same person gets on the KickVote list after that, the time spent will be 1 month followed by a whopping 2 months on the Watch List.