I have come to the US on a J1 Visa from 2008 - 2010 and used the tax exemption through filing form 8233 with regards to Article 22 of the India - US Tax Treaty.

Am now returning to the US from 2012 - 2014, will I be able to use the exemption from taxes again, or is there a 1 time limitation on such? Thanks.

Probably not, because there is retroactive tax provision if you exceed two years (24 consecutive months) on a the J-1 visa. Given the retroactive tax provision, it is hard to conceive that they would allow you to use the exemption TWICE for more than two years.

On J1 visa the exemption for two is available only once.