Some pages timeout really fast and log you out, such as the exchange web mail my work uses. It would be very useful to be able to right-click on a tab and be able to select "Configure Auto-Refresh".
This would bring up a dialog to configure auto-refresh for n number of seconds. Each refresh should also preserve any data you've entered into any form fields on the current page. Perhaps there are other configuration ideas that might also be added.
This would also be great for things that you need to keep an eye on like rainfall radar, ebay auctions, stocks and shares etc. It would be so useful and I would guess easy to implement (preservation of user data could come later - or not at all) I am surprised it isnt there already?