The accepted answer was originally correct but this seems to have changed as of October 18, 2013. A number of news items about this can be found all over the web and some semi-official websites have also been updated to reflect this change, e.g. this short-term stays / short-stay calculator from the Swiss federal government.
I was not able to find any authoritative source detailing the legal basis for this change. The Handbook for the processing of visa applications and the modification of issued visas linked from the Commission's website, while it has also been updated (file name is the same but this is not the document cited in the other answer), still contains a reference to EUCJ case C-241/05 and language derived from this case.
Also note that according to the EU commission the new rules are not applicable to citizens from the following countries: Antigua and Barbuda, The Bahamas, Barbados, Brazil, Saint Kitts and Nevis, Mauritius, and Seychelles. For these countries the old rules still apply because the visa waiver agreements still contain the older definition.