It is different from the 1.8T that is in the mk4 cars. More efficient and I believe it runs on regular fuel vs. premium. And emissions are better I imagine. Despite it having a turbo, its rated higher than the 2.5 for fuel economy. I'm interested to get some seat time in one. I'd be getting the 2.0T if I got a newer VW (or a TDI), but its a neat idea for a base engine.
For future reference, I hope they'll be able to run on 87 gas. Premium is now 40 cents higher than 87 in Wisconsin, so a 17% increase in fuel economy that is claimed (about 5 mpg) would pretty much be negated by the higher pump price of Premium.
I was just at my local vw dealer today and talked to my salesman about this. the only non-turbo motor will be the vr6 and the 1.8t will be about the same hp and 10 ft/lb torque more than the mk4 1.8t and run on 87 octane. All while getting 30+mpg.