By launching direct military action against the Houthi/Saleh forces in Yemen the Saudis are taking a long term risk.  Though they might be by far the stronger party at the moment it is conceivable that they might meet strong resistance.  It is hard to subdue people who have nothing to lose and the Yemenis are very poor.  They also live in extremely difficult terrain.  Until now the Houthis were respecting the Saudi border.  Now that the Saudis have attacked them they will have no qualms about operating in Saudi territory.  Given there is significant Yemeni/Houthi population in the regions of Saudi Arabia which border Yemen's northern border, the Saudis are leaving themselves open to a war which could end up being fought on their own soil.  The Saudis may rationalise that if the Houthis gain complete control of Yemen they will, given past history, be after their southern regions next anyway.  This may be true, but the international community would have been virtually unified in opposing one country attacking another.  By Saudi Arabia attacking first they have forfeited this moral high ground.
The Saudis do already have the support, perhaps even the encouragement, of the United States of America in their attack and perhaps they believe that this is the only voice in the international court of public opinion that matters so why not invade.  This is a fair point, but America's priorities might change in the future while Yemen''s position on the southern border of Saudi Arabia will not and now that the Saudis have broken the peace I am sure the Houthis will be eager to take the fight into Saudi territory whenever they can.

26-3-2015 
It has been an interesting day for two reasons.
1. Events in Yemen.
Suddenly the Al-Houthi's supported by forces loyal to the former President appear to be on the verge of taking control of Aden the former Capital of South Yemen.  Given that many pundit have been predicting the imminent break up of Yemen into its former independent parts of North Yemen and South Yemen this is a very significant development.  Particularly significant is the involvement of the former unifying president Ali Abdullah Saleh.  Now, while I do not put myself forward as an expert on Ali Abdullah Saleh, I will say that in unifying North and South Yemen to create one  nation Saleh achieved a feat which makes him one of the most successful national leaders of the twentieth century.  I note that Yemen's current troubles started while Saleh was seriously ill.  If Saleh is back in control of himself, and today's events suggest to me that he is, then those who are saying that 'there is no one who can pull Yemen back together,' might find that they are mistaken.  
Though if Saleh comes back to influence through the aid of his former adversaries, the Houthi's it could well spell worrying times for Saudi Arabia.
2. The Ukrainian President has sacked the powerful oligarch Igor Kolomoisky from the post of Governor of the Dnipropetrovsk region.  Given that Kolomoisky is seen as the man who was most influential in ensuring that Dnipropetrovsk did not join the pro-Russian separatist movement this rift between himself and the Ukrainian government presided over by fellow/rival oligarch Petro Poroschenko is very significant indeed.