Posted by Ybose at 06:21
The Ruling in Blindly Following
the Mathhab of the Shiites
Some people consider that it is an obligation upon the Muslim to blindly follow one of the four well known schools of Islamic Jurisprudence in order for their acts of worship and their deeds to be correct. Yet the Mathhab of the Shiites is not included amongst them, not even the Mathhab of the Zaidi Shiites. Does your Eminence agree with the absoluteness of this view, and thus prohibit the blind following of the Mathhab of the Shiites, such as the Imamate of the Ithna Ashriyyah? 
It is an obligation upon the Muslim to follow what came from Allaah and His Messenger (sallallaahu alaihi wa sallam), if he is able to infer the legal rulings himself; if he is unable to do so, he should ask the people of knowledge regarding what troubles him in the matter of his religion. He should make enquiries of the most knowledgeable with whom he is able to make contact, so that he may ask him, either in person, or in writing. It is not permissible for the Muslim to blindly follow the Shiite Imamate Mathhab, nor the Zaidi Mathhab, nor any other such like Mathhab from the people of innovation, such as the Khawarij  the Mutazilah,  the Jahmiyyah  and others. As for belonging to one of the four well known Mathhabs, there is no objection to this, so long as he is not a fanatical follower of the Mathhab to which he belongs and does not dispute (authentic) evidence on account of it.
 Ithna Ashriyyah: A large group of Shiites who believe that twelve particular Imams posses greater knowledge and powers than even the Prophets and angels.  Khawarij: An extreme sect, who claims that committing major sins take one out of the fold of Islam, and that those who do so, will be in the Hell-Fire for all eternity.  Mutazilah: A deviant sect, who introduced speculative dogma into Islamic beliefs.  Jahmiyyah: A heretical sect founded by Jahm bin Safwan, who denied Allaahs Names and Attributes.
Permanent Committee for Research and Verdicts
Fatawa Islamiyah Vol. 1 Page 330
Taken from http://www.fatwaislam.com/fis/index.cfm?scn=fd&ID=1138