There are individuals on the Cruze forum that are getting 50mpg out of their ECO's. Plus they are doing to their Cruze's what a lot of the Camaro owners are doing, MODing them to get more power. I see the diesel being a small power beast when it has been out a while and all the aftermarket comes online for it.
I have a 91 jetta TD and of course it smokes like all older diesels but I get 50mpg out of it on ever tank fill up. Plus I run for free in the summer when I use waste veggy oil.