I saw a press release from Intacct which invoked those words. I see fellow Irregular Susan Scrupski describe how her firm nGenera is 100% SaaS. The Office 2.0 conference I took part in recently had a session on Going 100% SaaS...and the conference itself was 100% SaaS. It was disorienting to not have agendas or slides anywhere but in the cloud.
I see Symphony, which offers outsourced R&D to many an on-premise software vendor, offer a seminar on how software vendors can transition to SaaS world - doing their part to make the world 100% SaaS.
Come to think of it, 100% SaaS should be easier than the 100% paperless world we have promised for ages...