"IMO some of the 100 share trades you see are not all done to manipulate the SP. In particular, if you trade through TD Waterhouse, in order to get a transaction at $9.99 you need to have at least 30 trades in the last 3 months"

This may be true for you and others but Anonymous and the like don't generally have to worry about $29 vs $9.99 trades. If you study these trades of 100 or so shares you'll see that most of the time they don't have to take a lower sp to sell but do. The timing is also strategic, meaning it is usually done at a sensitive time when the sp is developing momentum. These techniques are momentum breakers. Notice we are not seeing much of this lately for reasons which will soon be evident.