I just tried upgrading from 2.7 to 2.8 via the upgrade button in teh admin panel and i got this error:
Downloading update from http://wordpress.org/wordpress-2.8.zip
Unpacking the core update
Incompatible archive: PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature
i've updated 6 of my other blogs with no problems, including 1 other with the same theme and plug-ins..