The problem seems to be that many groups had never had to file Form 990 before, because their annual receipts were under $25,000. And they didn't notice the new law passed in 2006 saying that even these small groups had to at least file an "e-postcard" version of the form.
The LAST CHANCE date to file is: May 15, 2010.
For details, see Nolo's article, "Many Nonprofits Must File IRS Form 990-N to Stay Tax Exempt."
