Question Summary:
Is it Bid’ah to make Duā in congregation regularly after Fardh prayer?

Question Detail:

Is it bidat to make dua in congregation regularly after fard prayer?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Making Duā collectively after obligatory prayers is permissible on condition that one does not believe this to be necessary or mandatory. [1] It must be ensured that the audible Duā does not cause disturbance to those who are completing their missed prayers. [2]
For a detailed research on the topic, refer to the following link:
http://www.scribd.com/doc/31786440/Collective-Dua-After-Fard-Salat-by-MUFTI-IBRAHIM-DESAI   
 
And Allah Ta’āla Knows Best
Abdul Azīm bin Abdur Rahman,
Student Darul Iftaa
U.S.A.
Checked and Approved by,
Mufti Ebrahim Desai.