Corporate taxes for big and small

As a small business owner, I was stunned to read about Google's effective tax rate.  Clearly the opportunity is open to multinationals and can be completely legal.  But so much for the idea that these firms will contribute taxes to the US economy ... or that lowering the US corporate tax rate will result in a larger tax revenue.  Closing corporate loopholes may snare more revenue from small businesses, but if 12.5% is not low enough for Google, what is the floor rate to keep revenue in a country ?  Unquestionably, Google employs lots of folks in the US ... just making the point, via this article, that this is no simple issue.

http://www.guardian.co.uk/business/ireland-business-blog-with-lisa-ocarroll/2011/mar/24/google-ireland-tax-reasons-bermuda