It has been a late night out with the friends. You have had a fantastic time except for one minor detail: you haven't seen or heard from your 'special friend.' So why not send him / her a quick email to 'check-in?' Google has recognized this tendency and now offers Gmail Goggles. Essentially, you decide when you want the 'goggles' to kick-in: Friday morning after 1AM, Saturday morning after 2AM... whatever you perceive as your 'danger zone.' In order to send an email you have to perform some quick math and then send away! If you are an incredibly persistent person, a little math won't deter you, but it has the potential to save you from some bad decisions.
Sidebar: To turn on the Gmail Goggles features, click settings in the upper right hand corner; go to the Labs tab; click the enable radio button next to Gmail Goggles. Then go back to settings and pick when you want to enable the Goggs.