The newest Gmail Labs feature gives you a small red or green indicator next to contact names, aiming to help you avoid an Oops-it's-3:30-a.m.-over-there-sorry phone call.
The little red or green phone icon actually uses a broader guideline than just average sleeping patterns: it turns red when it's outside 9am to 6pm in the email sender/recipient's local time zone, indicating they're probably "out of the office." It's all pulled from your message headers, and if no time zone is specified in an email, the icon won't show.
I find it funny that my first post of the day indicates neither Adam nor I are reachable, but I'm also wondering how long it will take before that little red phone icon becomes an annoyance. Luckily, like all Gmail Labs features, it can be easily enabled or disabled from the Labs menu in your Gmail Settings area. Tell us what you think of the little time zone reminder in the comments. New in Labs: Sender time zone [Official Gmail Blog]