Ernie Els nearly won last weeks tournament while putting with a belly putter. It wasn't that long ago that Ernie complained about the belly and long putters being allowed on the PGA Tour, now he uses one but still thinks that anchoring a golf club should be banned from the game but his recent quote is "as long as it is legal then I will keep on cheating like everyone else".
While I don't feel that the length of a putter or anchoring a putter to your body should be banned my side saddle method of putting is completely legal and the USGA has already ruled on side saddle putting even recently changing the rule in a manner that makes it almost impossible to get a penalty called while putting side saddle.
Here is the rule and the exceptions to the rule it is rule 16.1-e
16.1.e. Standing Astride or on Line of Putt
The player must not make a stroke on the putting green from a stance astride, or with either foot touching, the line of putt or an extension of that line behind the ball.
Exception: There is no penalty if the stance is inadvertently taken on or astride the line of putt (or an extension of that line behind the ball) or is taken to avoid standing on another players line of putt or prospective line of putt.
As you can see if a golfer inadvertently stands on the line or stands on the line to advoid standing on another players line he is not violating the rule. So unless the golfer stands on the line all the time according to the rule side saddle putting simply cannot be called a violation.
Here is the most recent qoute from Ernie Els about anchoring a golf club to the body.