The announcement comes after a summit spurred by the sectarian division and tension between Saudis and Iranians over recent events in Iraq and Lebanon. The two countries represent two different sects of Islam: Iran is a nation of Shias, while Saudi Arabia is a Sunni nation. This has led to the two countries often serving very different political agendas.
The two are willing to put aside their differences, natually, to face larger enemies. Ahmadinejad and Abdullah were able to realize common views on Palestinian independence and issues surrounding Iraq. Ahmadinejad went on to say that "plots carried out by the enemies in order to divide the world of Islam were discussed" and that the Saudis had joined Iran in condemning them."
Hopefully these talks will mean that two countries currently at peace in the war-torn region will remain these way, different sectarian practices and poltiical agends or not. The two countries seem to have little in common but they both share a hostility toward the West that will probably keep them friendly for the time being.