I looked at the Yahoo! Hadoop 0.20 patch. One minor nit is that the internal config option name is different between this and the trunk patch. In the trunk patch, the option is distcp.skip.crc.check. In the internal patch it is distcp.skip.crc. Since this is a jobconf option, it may be better to keep these in sync. At the very least, it avoids confusion when Hadoop is upgraded to the trunk version.
Other than this, the 20 patch looks good.
Another point, (unrelated to this JIRA), is that the way the post-copy validation is done between trunk and 20 seems different. In trunk, this is done by a call to the API sameFile(). Hence, it includes CRC checks by default. In the internal 20 patch, this check is done only on file lengths irrespective of the option to skip crc checks. It is unclear whether this is by design. At any rate, this inconsistency is not related to this patch.