I'm also getting slow upload speeds using the smugmug upload in PM 4.6 on MacOS 10.5.6. It's not the transfer speed, it's the 'File sent -- waiting for remote acknowledgment' that's making the uploads take twice as long as the MacDaddy smugmug upload. Each 'remote acknowledgment' takes about the same time as the actual upload (for 5-8MB JPGs).
-Mike