Ha'aretz published an editorial saying that "everybody wins" with the US decision to sell $20 billion of weapons to Saudi Arabia and to increase defense aid to Israel to maintain Israel's military edge.
While Ha'aretz is perhaps right in the sense that Israel could not have successfully opposed the Saudi deal, this is hardly a "win."
Events over the past twelve months in Israel show how the next Arab/Israeli war is likely to play out, and by any reasonable measure this "evenhanded" arms sale is only a "win" for US defense contractors.
The Hamas coup in Gaza shows the fragility not only of the pseudo-moderate Fatah but also the strength of the fundamentalists, not only in the territories but throughout the Arab world. Saudi Arabia's royalty may be cozy with the US today but her citizens are most assuredly not. The House of Saud maintains order with repression (and a bit of bribery), and it encourages terror against other nations implicitly by continuously exporting Wahhabi-fundamentalism to mosques and schools worldwide.
The putative reason for arming the regime is to act as a counterbalance against Iran, but the lazy Saudis can't even maintain their own society without importing workers - they have no fighting ability to speak of, no matter how many high-tech weapons they have. It is also far from clear that in the case of a larger conflict between Iran and the West whose side their soldiers would be on.
It is very possible that the arms Saudi Arabia are receiving will only be used by terrorists.
The reason Hezbollah is thought to have "won" last summer's war is because the goal was not to defeat Israel but to hurt her, with rockets. This is the nature of an asymmetric conflict, where the nation who cares about its civilians is at an automatic disadvantage and international law only ends up hurting the nations that care about collateral damage. It is simply impossible to defend a nation against$20 billion of weapons in the hands of jihadists next door. There is no such thing as a "qualitative" advantage in an asymmetric war.
The Kingdom of Saudi Arabia will never use these weapons in any way that the US intends. But it is, unfortunately, likely that the weapons will be used.