I noticed that the preview images that google generates for their search results, are counted as a visitor. Is it possible to ignore those visits. If you want to test yourself, go to google webmaster tools, ask for a new preview image, and you will see a new visitor on your site with OS linux 1024x1024, browser chrome 9.0 and an unknown IP.
This should have been fixed in Piwik 1.1.
Can you look in your Apache log file and see what the full User Agent was?
Never mind. This has been reported as a bug to Google.