Now Google Maps' "MyLocation" is not exclusively available to mobile users but also to desktop users. This feature does exactly what you would think: marks your current location.
However, you've got to be using a compatible browser. If you haven't upgraded to Firefox 3.5 or Chrome 2.0 (or any browser installed with the current version of Google Gears), then do it before you try to use the feature, because without any of them it won't work properly.
Then when you load Google Maps, look for a teeny tiny new box between the zoom in/out bar and the compass circle. Click that box and you'll be prompted to give permission to share your location.
Up until now, desktop's MyLocation do not display the famous blue circle that uses in the mobile version to find your specific location. This means that while it says to you the area where you are, it cannot tell the specific point where you are.
Google uses nearby wifi points to determine location, but it may not be able to provide one every time.