I have personally found with the Zed that it is seriously dependant on how heavy you are with your right foot, and what sort of driving you do. (I know this is true of all vehicles but the difference in figures in the Zed is pretty large)
To give you an example, for me personally....
On my daily commute, which is a 72 mile round trip, mostly motorway and dual carriageway (Southampton to Ringwood) with a little bit of around town driving after work (gym, girlfriends etc)
heavy right foot : 22-24
being conservative : 28 - 29
When I had a week off, and spent all week driving around town, lots of cold starts etc :
heavy right foot : 14-16
being conservative: 17-18
I think it is something you should consider carefully if buying a new Zed that you will be using for commuting. I love mine, makes me grin everytime I get in it, BUT I put alot of miles on her (11000 in 9 months, but i've worked away and left her on the drive for 3 of those), which is working out about £300 a month on fuel.
Then take into consideration tyres, brakes, and more importantly the effect of that many miles on the front bumper of your beloved Zed (Don't talk to me about stone chips, my front bumper looks like it has some weird disease) before making your decision.
Still wouldn't change her though :-D
-Dave