Anyone remember when on Friends Rachel got drunk and left Ross a voicemail telling him she had "closure" over their non-existent relationship? Well, that's called "drunk dialing." In a "not-that-useful-but-at-least-offbeat" Gmail Labs "feature," Google is introducing Mail Goggles, which aim to prevent you from "drunk emailing."
To access it, you go into Settings, and then the Lab subsection. Scroll down and you'll see it (by default it's disabled). Enable it, and now you're "protected" from sending an email you're going to regret, whether it's because you're intoxicated or just plain tired.
When enabled, and when the time is right, you'll have to answer a few math problems before the email will be sent.
What do I mean by "when the time is right?" The feature only works during certain periods. Once you enable Mail Goggles in Labs you will be able to change that period in your General Settings tab. You can also change the difficulty of the question, if you want to challenge yourself.
A nice albeit questionably useful feature, but I think they need to add such a feature on their Android platform. After all, someone's probably more likely to send an SMS from their cell phone while drunk than boot up their PC and send an email.