I believe The_Banking_Scot is spot on with his post. Neither the US Customs and Border Protection nor the US Department of State mention more than a ninety day limit per tourism or business entry to the USA in their pages; no mention is made of any limit on how many =< 90 day visits may be made within any period of time. It is mentioned your passport must be valid for six months beyond your entry date to the USA.

US Department of State Visa Waiver Program page

CBP Visa Waiver FAQ


U S Citizenship and Immigration Services Nonimmigrant Visa Classifications

You can download the PDF version of the Visa Waiver Program Traveler Guide by right clicking (or otherwise saving the target file) here.

No disrespect to anyone here intended, but I highly recommend getting something definitive in writing from CBP agent if there is any variance in what you are told (like a 180 day limit) with what is written on the official websites - and as opposed to relying on differing opinions on FlyerTalk or the idea that US VWP might have similar requirements to France's maximum stay requirements, or anyone' else's.