Colette Kamps, CPA of Nonprofit GPS has some background on how long it is taking the IRS to process applications for exempt status.
In her post, How Long Does it Take to Get IRS Approval for Tax Exemption?, she says:
If you go to “Where Is My Exemption Application?” at the IRS website, you will see that the IRS is currently processing applications they received in November 2011, so 11 months ago.
She also gives a framework for simple requests, when some additional info is needed, or your application generates lots of questions.
The post also highlights some of the most common reasons for additional correspondence regarding the application. Double check those items to reduce the chances of delay caused by the IRS having to clarify something.
Check out the full post for more info.