this is only as information, not a request.
I my test site I have commented the "if (is_multisite()) return;" in your plugin and, up to now it's working fine.
BUT, I did a very small modification in wp-includes/functions.php because I was not getting the specified "upload path" when uploading in a secondary site. But the "upload path" was correct when uploading in the main site. This problem I had right from the beginning, without your plugins.
WP version: 3.2.1
$main_override = is_multisite() && defined( 'MULTISITE' ) && is_main_site();
$main_override = is_multisite() && defined( 'MULTISITE' );
I do not pretend that this modification may not cause eventual problems, but for the time being it did solve my issue with the secondary site's "upload path" not being passed properly. And I did not find the relevance of testing
And, so far, in this condition, your plugin is working fine in multisite.
Again, this is information, not a request.