I'm not exactly sure why the docs recommend GIF/JPG. Perhaps it's just an area that needs to be updated to match the times. I've been using PNG nearly exclusively without issue for a few years now.
Maybe there was a time when some browsers didn't understand the PNG format. But I've never had a problem with it myself.
Helpful and Handy Links
Proper PNG support was added to Internet Explorer in version 7. If you have to support IE6 (which I hope you won't have to) you must be very careful with PNG's with transparency. If you only support IE7 or higher you can use PNG to your heart's content.
Thank you all for your quick reply.