[nailer]

Simple:

(time taken to close window ) x (amount of messages per day)

Compare 'Alt-F4, up arrow' with 'up arrow'.

Making the text width narrower also increases your reading speed, around 6-12 words per column is apparently the ideal width and is the basis for all newspapers, and since suck.com started it in the late 90s, the majority of websites.

[Kejistan]

Thanks for the explanation!

I'd also like to take the time to point out that you can get similar functionality using the vim-style keyboard hotkeys in gmail: j/k to move to the next/previous conversation.

[nailer]

No prob. Keyboard shortcuts are useful when they work (j and k don't in Chrome 5 on my laptop, OS X 10.6), but a lot of users use the preview bar to skip messages too.