I use a 50/50 mix of RO to tap water. I am also no expert in reading water profiles, but since I've started doing that, my beers have improved noticeably. There seems to be a balance there that, although I don't completely understand it, works well for just about any beer I brew. I do think that if I spent more time on learning water chemistry I would probably be brewing even better beer, but I'm not getting any complaints. That's what's most important, unless you are brewing for competition.
John and Colin's book on water can be an invaluable tool. I have it, but just haven't got to curling up next to a fire with it yet.