This review has just been pointed out to me:
http://www.pcmag.com/article2/0,1895,1759560,00.asp

One bit in particular is interesting:
But the ZonePlayer does the opposite as well: It can play the same music throughout the house, perfectly synchronized. Even though that may seem drop-dead simple, other hubs don't do it.
This seems a little unfair on the Squeezebox which also does it, maybe someone should point it out to them!

Andrew