Usability 
Here's another cool webapp from Dmitry Namiot, the developer of mobile web based contact card service, Mobile Share (review). This one lets you send geocoded mail. It works with any browser that exposes the W3C geolocation API, currently iPhone, Android, Maemo and possibly others. The geolocation API has a lot of support from Google and others and I expect it to be a standard feature on mobile browsers in a few years.
Geo Mail provides an email form where you type your message title and body and choose whether you want to include a link to either a scrollable or static Google map or just your latitude and longitude. When you hit the "Send" button GeoMail opens your device's default Email app with the message and location information pre-populated, all you have to do is specify the recipient and send the email.
This seems like it would be handy for impromptu meet ups with friends who might be unsure of exactly where you were or how to get there. Anyone needing help with the location could click the link to open a mobile friendly map in their browser.