The USGA Rules site has an update to the rule that caught Stewart Cink at the Zurich Classic earlier this year.  Too little - too late for Cink.

His ball came to rest outside of a fairway bunker, but he had to step into the bunker to see where his best stance would be.  That shot ended up in a greenside bunker.  He raked his footprints from the fairway bunker before moving to the greenside bunker - and broke Rule 13-4, then signed for an incorrect scorecard when he didn't include the penalty strokes.

Rule 13-4 says: “Except as provided in the Rules, before making a stroke at a ball that is in a hazard … the player must not:

a. Test the condition of the hazard or any similar hazard; …”

Since then, they have "reconsidered" that rule and released a new decision and a statement.  Better late than never...unless you're Stewart Cink and this silly rule bites you on the backside.

The R&A, USGA Announce Position On Raking A Similar Hazard

The Joint Rules Committee (JRC), consisting of representatives of the Rules of Golf Committees of The R&A and the United States Golf Association, have issued an interpretation of Rule 13-4a with respect to testing the condition of a similar hazard (whether a bunker or a water hazard). At its customary April meeting, the JRC reviewed several issues relating to Rule 13-4 (Ball in Hazard; Prohibited Actions), including some that were carried over for resolution from the previous quadrennial Rules revision cycle. One such question was whether a player whose ball lies in a bunker may smooth sand to tidy up another bunker, even though he had not made a stroke from that other bunker.

After discussion, the JRC agreed on the following position, effective immediately:

Rule 13-4a prohibits a player from testing the condition of the hazard in which his ball lies or a similar hazard. Yet Exception 3 to the Rule, which was introduced in 2008, allows a player to test the condition of one hazard after playing from that hazard into a similar hazard. Although Decision 13-4/0.5 lists smoothing a bunker with a rake, club or otherwise as an example of testing the condition of the hazard, the Etiquette Section of the Rules of Golf provides that "Before leaving a bunker, players should carefully fill up and smooth over all holes and footprints made by them and any nearby made by others."

It is not the intent of Rule 13-4a to prohibit players from practicing the proper etiquette of the game when more than one bunker is involved. Therefore, when the player's ball lies in a bunker, it would not be a breach of the Rules if the player were to smooth the sand in another bunker, provided (a) the smoothing is for the purpose of tidying up the bunker, (b) the smoothing does not breach Rule 13-2 (Improving Lie, Area of Intended Stance or Swing, or Line of Play) with respect to his next stroke and (c) there is not a reasonable possibility that the smoothing could affect a subsequent stroke by the player.

If the player were to smooth sand in the bunker in which his ball lies prior to making his first stroke in that bunker, he would be in breach of Rule 13-4a.

While the JRC does not normally make public the results of its deliberations outside the updates of the Decisions on the Rules of Golf every two years and the Rules of Golf every four years, The R&A and the USGA do informally answer questions about the Rules of Golf as those questions arise. Questions have arisen in connection with a recent ruling involving Stewart Cink at the Zurich Classic of New Orleans. In that situation, the player incurred a penalty for smoothing sand in a bunker from which he had not made a stroke, when his ball lay in another bunker -- a ruling that followed the USGA's Rules of Golf Committee's position at that time. To avoid such an act being a breach of the Rules in the future, the JRC has decided to make public its agreed position on smoothing a similar hazard.