Long tail keywords are normally keywords with 3 or more words. To track it down I used the following regular expression: [^\s\+]+(\s|\+)+[^\s\+]+(\s|\+)+[^\s\+]+
Steps inside Google Analytics. Traffic Sources->Search Engines->Google->Non paid
On the filter keyword [containing] I input the regular expression: [^\s\+]+(\s|\+)+[^\s\+]+(\s|\+)+[^\s\+]+
After I just tracked down the last 3 month number of visits with and without filtering the long tail and calculated the % value of the longtail.
long tail keywords/total organic = % of the value for the long tail
5 minutes and I realised that mayday update did *not* influence my sites long tail keywords.
Hope that helps and if someone knows of a simpler or more effective way to do this I would love to know.