When I finally get around to getting an A3 printer and A3 scanner, I'll be principally looking at HP for starters, absolutely no problem with OSX for me.
Me neither (but, then again, I'm not Richard Barrett, which is a shame overall I'm sure but does seem to have this one particular advantage). I have an 11x17 (approx. A3) printer from HP, the DeskJet 1220C, that aside from the fact that it can be difficult to cajole the large-format sheets from going through the mechanism in a purely rectilinear fashion has been fine for my needs. I don't tend to print out music with it, though, only text, so I don't know how good it would be for high-res stuff.