I've been getting about 29 mpg on my 240D, mostly highway at 70-75. That's the average over about 6 fill-ups over the past couple months.
I usually leave the AC off, for a number of reasons (#1, it's cold in my office, so sitting in a hot car on the drive home is refreshing. Really! #2, the AC doesn't work so well anyway, it's time for a recharge. #3, come on, it's a 240D, I have to floor it to get anywhere anyway, it's even worse with the compressor running...)
The wife's '00 New Beetle TDI gets exactly 39 MPG, with about 95% 80mph highway driving. We've kept a record of every fill-up since we drove it off the lot. The sticker said 44 (city) to 49 (highway), so I'm going to bug one of the service advisors next time we take it in for scheduled maintenance.
'83 240D, 252k miles
'00 New Beetle TDI, 7000 miles