Lots of little stuff and a few bigger things. There are two good places to get all the info. One is the USGA website. Look at the new rule book that is online. Starting on page 6, is a description of the principle changes. Another is go to
http://www.middleatlanticga.org/. On the right side is a link to a PDF file that Lew Blakey put together that compares the old wording with the new wording of all the changes.
Here are the highlights:
As Bill said, the biggest is that you are penalized for playing a wrong ball anywhere on the course and that correspondingly you are allowed to identify your ball anywhere. One additional piece of wording that was put in is that it must be "necessary to lift the ball in order to identify it". In other words, some of these guys who are lifting their ball all the time had better have a good reason to keep doing it. (See Rule 12-2 and 15)
Advice on yardage is no longer a penalty. So, if a player asks how far your ball is from the hole you can tell them and nobody gets penalized. Same if they ask how far their ball is from the hole. This allows range finder information to be shared if they are allowed.
The penalty for hitting a shot and having it hit you, your equipment, caddie, partner etc has been lowered from two shots/loss of hole to one shot. Jeff Maggert might have inspired this rule with the shot at the Masters that rebounded off the face of the bunker and hit him. (See Rule 19-2)
The rule for carrying but not using a non-conforming club has been changed from DQ to the same as carrying 15 clubs. This might have been inspired by Kevin Stadler's DQ at a PGA Tour event for having a club with a bent shaft in his bag.
Lost Ball - An additional way a ball is lost when you put another one into play via stroke and distance. In other words, if you hit your second shot, can't find it and then go back and drop a ball, your first is lost as soon as you drop the new ball rather than when you hit it. This clarifies and somewhat reverses the change from 2004 which opened lots of holes. Note, this only applies if you are playing under stroke and distance. If you are dropping under one of the other options for a ball lost in a hazard and your ball is found before you hit the new one (and inside 5 minutes) you pick up the new ball and proceed with the original one (might drop in a different place based on the original ball's location.)
The Exceptions to Rule 13-4 (Ball in Hazard; Prohibited Actions) were modified and a third exception added. Exception 2 was made friendlier. If you hit your shot in a bunker and the ball is still in the bunker, you may rake and are only penalized if you improve the lie for that next shot, not any shot after that. The third exception says that if you hit a ball from one bunker to another one, you can do anything in the first bunker. This was inspired by Vijay Singh taking a practice stroke in the first bunker when his ball was had gone into another bunker.
Added the note to allow range finders under local rule. This was a decision on 2006 and moved to the book in 2008.
Substituting a ball modified to remove a double penalty for simultaneously wrongfully substituting a ball and playing it from a wrong place.
No penalty for standing on or astride your line of putt inadvertently or to avoid someone else's line. This was a decision and moves to the book.
Flagstick that has been removed and laid on the ground can now be moved if a ball in motion might strike it.
The term "Reasonable Evidence" has been replaced for balls possibly lost in a WH, obstruction, casual water, or GUR with "known or virtually certain" This was the way rules officials were being instructed to rule and now it is more clear to the players.
Clubs may be adjustable as approved by the USGA. This allows screw-in shafts etc.
And finally the most important (since I was one person who pointed it out to the Rules Committee
) is that you aren't penalized if you are searching for a ball in an obstruction and your ball is accidentally moved.