We had a Labor certification case filed for an IT professional. The requirements were Bachelor's degree and 5 years of experience. We filed I-140 under EB-2 category. After approximately 8 months, USCIS sent us an RFE saying Bachelor's plus five years would not qualify under EB2 unless the experience required is progressive in nature. We knew that USCIS was wrong under the circumstances of the case, but an argument with the government was unnecessary because the EB-3 priority dates were then current.
This entry is now old law. The new law is at http://www.immigration.com/blogs/i-140-ead-regulations-effective-17-jan…
5 November 2015: After some flip flops, USCIS has gone back to allowing carry forward of priority dates even if I-140 is revoked by employer - as described in this discussion. So, we are good for now.