Just tried 3 different ways to download 'wordpress-3.4.2.zip' and two ways to unzip it onto an iMac OS X 10.8.2 w/Mountain Lion.
Both Apple's Archive Utility, and WinZip for Mac, fail to expand the downloaded file.
Archive Utility reports: "Unable to expand 'wordpress-3.4.2.zip' into "Downloads".
(Error 1 - Operation not permitted.)
WinZip for Mac reports: "Fatal error: End-of-central-directory signature not found. Either this file is not a Zip file, or it constitutes one disk of a multi-part Zip file."