The first time I heard this phrase was at work. I helped out someone and when I was finished, he remarked, "sweet as." I did not know how to reply to that, so I just let it slide, all the while thinking... "sweet as what?" Ever since then, I have received that comment a couple more times. A quick google search revealed that "sweet as" actually meant "cool", or "awesome", or in the way I received the remark, a sort of "thanks".
I do not hear it that much, actually (save for a more recent ad campaign for Bluebird chips, now you hear "sweet as" on radio and TV). I think it's a quote more readily used by the younger generation though. I would more likely hear "cool", "wonderful", "cheers" and "that's fantastic!" from my peers.
Right now I'm stuck with saying "great" or "nice" but when I'm with Filipino friends, it becomes "ows?" and "ayos lang" :-)