Google enabled a way for webmasters to set a geographic target for their site. So if you want to tell Google, most of my visitors are from a specific area, you can do that. This way, if someone searches in a specific area and Google knows it, Google can serve up your site higher in the results for that user.
But what if a good portion of your target users are from a specific location but a large minority is not from within that area? Should you set your geographic area?
Setting your site's location information to Austria will help ensure that it will be returned in results for "pages from Österreich" searches. If your site is currently being returned for "the web" searches on google.de, it will continue to do so even after you've set your site's location information to Austria.
This does help but it doesn't give me the full picture.
There are more questions in the thread and hopefully we can learn more from Google's responses in that thread.
Forum discussion at Google Groups.