How accurate is Google's My Location?

I've done some tests (with the help of some colleagues) with the My Location service of Google mobile maps. We know that the service works based on cell-id, means that there is cell-id database at google which maps the cell-ids back to coordinates. Question is: How accurate is the database? To answer that, we did some measurements in the 2.5 G network in germany.
We just compared our current location (via GPS) with the result of the My Location service and calculated the distance. We did 132 measures.

Here's the result as a graph:



To summarize, My Location is 707 meters inaccurate on average.
80% of the measures are less then 1075 meters accurate.

So this is (of course) far away from GPS based LBS, and it depends on the use-case of a service if this is sufficient.