1. Now that people have wider and wider monitors, make an option for the skinny left column to stay where it is, the list of messages to be full-height in the middle, and a full-height window on the right for the message you're reading. This is especially useful with these large laptops that have a lot of width and not much height.
2. Instead of being able to flag messages or unflag them, why not make like a dozen different colors/symbols and allow users to assign names to them--sort of like the different colors on Yahoo! calendar?
3. It takes six clicks to decline and block a random (essentially always spam) chat request. First, you should be able to right-click on the tab and neutralize it permanently with one click. Also, and much more importantly, there should be an option that all chat requests can be ignored if the user is not already in your contacts. Skype has this, for instance.
4. You can cut and paste a message (i.e., move it), but you can't copy and paste it. Why not? Some users might find it useful to have a folder of specific messages without giving up the original location. Pretty much everything else we do with documents has this feature.