wait for ADB and he'll give you his take on maple....
I have backings in maple -ash and hickory besides boo.
HAven't tried the maple or ash yet.
Yup, hard maple is great backing wood IMO. Can't recall any failures with it. I've used it with yew to make warbows up to 120#. I also made a 74# maple backed ipe flatbow. Also used it with almost every compression strong belly wood there is, including: ipe, osage, yew, cherry, jatoba, yellowheart, blah, blah, blah. ELBs, flatbows, shortbows, longbows. You get the idea... I like it. All about the grain, of course.
That being said, I also like hickory and ash for backing wood. If done properly, any of these woods will work fine.