I admit I didn't read this entire thread, so if this has already been mentioned, forgive me... But, one smallish thing that I'd really like to see would be to have MC stop using the IE control when displaying web content. I think there are other web rendering engines that would be much more capable, and would give us better options for font/image scaling and a better user experience. I also prefer to keep my IE engine locked down on my computers (I set the security settings on IE to "high" since I never use it and that helps to protect Outlook and Word and other apps that use the built-in IE engine), but this makes MC's web content unusable.
Along the lines of the "fit and finish, and polish" comments above. Plus, it would help further "OS-independify" MC.
There are two very good options available for web rendering engines (Gecko and WebKit). I think the license and features available for WebKit makes it the ideal choice. If Apple can use it to build Mobile Safari, and Google can use it for Chrome, then I think MC could probably do something very nice with it.