How will the unrest affect the countries of the Middle East? Saudi Arabia and Yemen.

Yemen is in turmoil and its position is worse than any other country faced with upheaval, since the wounding of Yemeni president Ali Saleh during a June 3 attack on his Sana palace compound will likely lead to regime change in his troubled country. Although reports from Riyadh, where he is being treated for his injuries, suggest he wants to return home soon, Saudi Arabia, other Gulf Arab countries, the United States, and Britain all want him to give up power. From Washington's perspective, Yemen has emerged as al-Qaeda central and a concern that rivals Afghanistan and Pakistan.

Saudi Arabia, has tried to keep tabs on the quickly splitting Yemen, but has on a number of occasions got a bloodied nose from confrontations, They have now withdrawn their locally backed leader  president Ali Saleh from the area, this leaves the possibility of a Yemen in the future breaking into tribal provinces:

though Saleh's own authority often did not extend far outside of Sana. Yet in the absence of political reform and reconciliation, an apocalyptic scenario could emerge under which Yemen collapses into four parts: Sana and its immediate environs; a Houthi-controlled pocket in the northwestern mountains; the former South Yemen around the port city of Aden; and an al-Qaeda region in the center, perhaps with access to the coast linking it to the already-failed state of Somalia. 

it should also be noted that the Yemen is in the middle of a catastrophic drought, their water aquifers are quickly running dry, there is little for people to drink and even less for agriculture, so again expect to see a mass exodus from the area, which will compound the other countries in the area. All the unrest and likelihood of a failed state will lead to the need for greater international presence in the area, as the Bab al-Mandab Strait between the Red Sea and the Indian Ocean will become an increasingly dangerous place to ply trade through. It is where Europe gets their oil from and trade from te far east too, so all have an interest in a stable Yemen, not just Saudi. Iran on the Other hand have been pushing for greater instability and influence in the area, but that will come to naught as the area splits into tribal regions diminishing any possible returns from its investments.

So all in all the future of Yemen is bleak and has little positives for its population, which is growing at one of the quickest rates of any place in the world, all unsustainable.