the IRS gives new filing thresholds for non-profits, starting in tax year 2008. (Note on tax years: most of us finished tax year 2007 in the summer of 2008, and we're now in tax year 2008, which will finish in summer 2009 and the return will be due in fall 2009.)
The EZ threshold goes up to $1mil for next year, I think because the full 990 was revised and is harder to do; it then comes down to $500k in 2009 and $200k in tax years 2010 and later.
In tax year 2010, many PTOs may be able to file 990N, because that threshold increases to $50k.