I frequently drag links from browser windows to e-mails and instant messages and am absolutely obsessive about adding cover art to all of my music in iTunes; for these reasons, I would love Safari’s click-through behavior to be changed in areas related to these two tasks.
Being able to drag a link from Safari’s address bar or an image in a webpage without having to depress the Command key would be nice. Neither of these actions are potentially destructive and both are easily reversible, meaning they comply with Apple’s click-through guidelines.
While re-reading the click-through guideline, I noticed that they claim click-through resizing of windows provides “greater efficiency,” but it also requires the Command key, so the efficiency is rather reduced by having to hold a key down. Given how small the window-resize handle is, it could be probably made directly click-through aware without causing problems. Testing might prove otherwise, but that is up to them!