Google has announced that it's adding the "My Location" feature found on the mobile variant of Google Maps to the full-on browser version.
If you log in to Google maps with a supported web browser (Chrome 2.0+, Firefox 3.5+, or anything else that supports Gears) then you'll see a button on the left hand side of the map, above the Street View marker, but below the navigation wheel.
Clicking that will take you to exactly where Google thinks you are. That's worked out by using the W3C Geolocation API, which looks at Wi-Fi networks around you and your IP address, to determine where you are.
If you're worried about privacy, Google promises that it'll never use your location without your permission and you can always retract that permission. Go and give it a shot, and let us know how accurate it is for you.