If you're a world traveller, or even if you're travelling abroad for the first time and need absolutely everyone to know, Gmail now offers an option to include your location in the signature.
The Google Labs-based (beta) system works by reading your IP and guessing your location, much in the same way that websites track the locations of their readers. (Yes, we know where you live. Bwahaha.) But if you install Google Gears' location module, Gmail's location tagging system will be even more accurate, using Wi-Fi triangulation to locate your position (you know, like the original iPhone).
I actually love the idea, were "from my sagging couch in my tiny jail cell of an apartment" not the sad global source of 90% of my diatribes (I'll let you deduce the location of the other 10). [Gmail Blog via Lifehacker]