I did a quick google and found http://www.ahla.com/content.aspx?id=35603 which says that 40% of guests are on business and 60% are leisure travelers. This data is for the the USA for 2012.
Seems believable. I just caught an interview on television earlier today with the CEO of a luxury worldwide hotel, and he said leisure clients went up from about 35% to 45% in the past decade, so it's a growing focus for them.