Man, what HAVEN'T I used for a PA? Ive even used guitar heads and cabs as a PA. If you can fire it up and hear out of it then it works!
One of my favorite ones was when we used a Mackie into a Trace Elliot guitar head and powered 2 8x10 Kustom speaker cabs with it. Man those were the funny old days. Ive even used Marshall 4x12's as PA speakers.
My "ghetto" PA story - Back in HS, my band used some Radio Shack mics into a RS mixer. The mixer's output went into the aux in of my Aiwa bookshelf system. I had the little dinky speakers up on stage with us. It sounded awful!