Don't know about 'yay', but I got into trouble in this forum by snootily (or so it was, not unreasonably perhaps, supposed) commenting on the use of 'yup' instead of 'yes' in a posting on another thread. I genuinely wanted to know why people (and the poster who ticked me off was one of several) seem to prefer this usage, at any rate online. I often say something like 'yup' (or 'yep' or 'yeh') myself, but would never think of writing it, even in an informal communication. After all, it takes just as long to type as 'yes'. Is 'yes' perceived as prim or buttoned-up or English or what one's granny might write or uncool? Is the use of 'yup' a convention of cyberspace? Please enlighten me, somebody!