I'm not sure if this is even appropriate here, since it's not really WordPress' fault, but there's a bug in PHP 5.2.2 that prevents XMLRPC from working properly. Basically, $HTTP_RAW_POST_DATA is never set, even when called via POST or with the config option set to always be on.
It's possible to work around it in WP 2.2 by adding one line to the beginning of WordPress' xmlrpc.php file, right before the first mention of the variable.
$HTTP_RAW_POST_DATA = file_get_contents("php://input");
It's apparently fixed in the PHP CVS, but who knows how long it'll be before 5.2.3 comes out.
Anyway, I don't know if you'll want to include a workaround for a single-version bug (though this is the most current "stable" release) or what impact this would have running on other versions of PHP, but I thought I'd post it just to convey the info.
