Gmail adds cancel send button

Learned this evening - just after sending two emails that had errors and had to be followed up with corrections - that you can now add a "Cancel Send" button to gmail. What this does is add in a small delay of up to 30 seconds (depending on settings) before sending it to the recipient; if you press the undo link that comes up (next to the "your message has been sent" info) before the time is up it cancels sending and returns you to editing the message.

The setting is in the cogwheel menu under "settings" - I think it will occasionally be very useful.