Hizbullah and Assad

Porous borders and tactical retaliation have led to Lebanon's slowly getting drawn into Syria's civil war.  Now, Hizbullah's openly committing to the fight on the side of Bashar al-Assad pulls it from the fringes to the center.  Hizbullah leader Hassan Nasrallah portrayed Assad as a critical ally against Israel:

Mr. Assad has called the rebels stooges of Israel and the United States, and Mr. Nasrallah, in his speech on Saturday, echoed that theme, portraying Hezbollah’s military venture in Syria as a fight to “immunize” Lebanon from the Israeli invasion he said would surely follow if Syrian rebels prevailed...

He evoked Hezbollah’s tenacity during its 2006 war with Israel, signaling that the organization considered the fight in Syria to preserve Mr. Assad and the crucial conduit he provides for weapons from Iran, as important as its founding mission, opposing Israel and driving it out of Lebanon. 

One effect this could have is to entrench sectarian views of the Arab Spring.  Syria's uprising is hugely popular with Sunnis around the region, and for a major Shi'ite force to openly side the the Assad regime will deepen the suspicion of many Sunnis that Shi'ites are not a full part of the Arab world and its causes, and may be actively opposed to them in ways that favor Iran.