The IPG states:

A Caution is a verbal admonition to a player. Cautions are used in situations of minor incorrect play or disruption where a quick word can easily correct the behavior or situation. No extra time is required for a Caution, as any Caution that takes more than a few moments to resolve should be upgraded to a Warning.

The Annotated IPG states:

“Caution” is the term we use for a quick verbal correction to a player. Generally, these are used for “little” things. Shuffling in your lap instead of on the table, not announcing life total changes, or if a judge immediately steps in and corrects a player for playing a land tapped after an Orb of Dreams was destroyed. If a play error takes more than a few seconds to correct, assign the appropriate infraction/penalty instead.

In these examples, is it correct to give the player a Caution only and not a Warning?

1. A player plays a land tapped even though the Orb of Dreams was destroyed last turn?
   
2. A player does not reveal the top card of his library even though he controls a Courser of Kruphix?
   
3. A player puts a card exiled by Assert Authority into his graveyard?
   
4. A player untaps a creature tapped with Crippling Chill and then proceeds to draw his card from the turn.
   

In all cases, assume that a judge was watching the match and stepped in immediately when the error occurred.

1) uhhh… didn't you quote that very example?
2) I find that the opponent usually reminds them soon enough; if not, it's fine to remind them, at least the first time or two
3) and 4) I'm not as comfortable ignoring these, although a polite reminder is probably OK the first time; in both cases, the opponent is likely to point out the error, since the effect is part of what they gain.

Philosophically, it's kind of like minor violations of traffic laws. Most of the time, nothing bad happens, and you won't get a traffic ticket from a cop. However, if the violation is at least partly to blame for an accident, then you're likely to get a ticket. Also, if you persist in ignoring a law, or do so in a way that could endanger others - even if no accident actually occurs - you're likely to get a ticket. And, of course, if the cop is having a bad day, feeling grumpy, or just a real hard-nosed enforcer of every little violation - you're going to get a ticket you probably don't deserve.

Let's not be that grumpy, hard-nosed cop, OK?

d:^D