In the 415 podcast Mike talked about Googles new ‘goggles’ option which if you set asks you maths questions before you send an email at times you might have had a drink or seven. Personally I have never had a problem with sending email under the influence (although I could use a feature like that for my mouth).
There are a number of other interesting options that you can find in the “labs” section of your Gmail settings. Ranging from as bizarre as an option to play Snake within your mail window, to adding “mark as read” as a button instead of a menu item. Makeuseof.com has a list of 5 features and some instructions on enabling them. My personal favorite from their list is the ‘forgotten attachment’. This option flags up a warning if you have the word ‘attach’ or a variation in your message and no attachement in case you meant to attach something and forgot. I do this all the time and wish I could get this option for my work email.
Some other options worth looking at are ‘custom keyboard shortcuts’ and ‘mouse gestures’, which are self explanatory; and ‘Superstars’ which give you multiple star colours and other icons, which can be very useful for managing your starred email with a bit more granularity.
It goes without saying that all the labs options are beta.