We were recently retained at the I-140 Appeal stage for an I-140 denied on grounds of fraud/willful misrepresentation. USCIS denied the I-140 citing inconsistencies between the ETA 9089 job requirements, the advertisements, and a subsequent letter sent by petitioner with an RFE pertaining to the job requirements. Due to what USCIS termed as "material inconsistencies," the I-140 was denied on the grounds that the labor certification submitted was gained through fraud or willful misrepresentation of a material fact.
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.