Just checked this out as my brother (teledan) mentioned this thread.
I have a 2003 TDI Jetta with 200k on the clock and it still runs amazing. Always put high quality, full synthetic oil in it that matches the recommended specifications and you won't have any problems in that regard. I perform an oil analysis on every oil change just because I'm geeky like that and there's no problem running it 15k+ miles per oil change with the right oil.
Just a clarification on the auto vs manual debate though... it sounds like people are mentioning two very different cars on this thread 1) 1999.5-2003 Jetta TDI and 2) 2005.5-present Jetta TDI (more comparable to the Audi A3). These are two very different beasts with different body styles (the '10-present has yet another body style). As was said, there are automatics that I would never buy in a VW TDI. In the various forums online they refer to these as "slushboxes" because they are your standard planetary gearset, ton-of-hydraulic-fluid automatic transmission that seem to fall apart after about 150k miles. Not to mention, because of the inefficiencies of planetary gears with so much fluid "sloshing" around inside, they get noticeably worse gas mileage than a transmission with a proper clutch.
HOWEVER, VW (and Audi) make other amazing automatics that are called DSG transmissions (stands for Direct Shift Gearbox) and those are amazing technological pieces of work. Porsche and Audi have been racing DSG transmissions in their rally and street cars for decades and it's finally trickled down to the VW and Audi passenger cars. Basically a DSG is a transmission with two clutches and the ability to have two gears selected at once (almost like two transmissions working in tandem). For example, you start off in 1st gear with the clutch engaged, (we'll call this clutch #1) while the other half of the transmission is already in 2nd gear with clutch #2 disengaged. As soon as you hit the proper RPM's (and throttle position, etc.), clutch #1 disengages and clutch #2 engages at the same time so you get an immediate shift from 1st to 2nd gear. Then the transmission puts the first half into 3rd gear in anticipation for the next gear change from 2 to 3 and the process continues. They're amazing to drive and feel oh-so-good with the solid, lightning quick shifts. Because they are essentially a computer controlled manual transmission, they get as good (or better) gas mileage than you could get with even a regular manual transmission (short of hyper-miling techniques). If the car you're looking at is a 2005.5 or newer and it has an automatic, don't let that deter you UNTIL you determine if it's a DSG transmission or a slushbox. Some DSG's (the older ones with wet clutches instead of dry) do need a somewhat technical fluid change roughly every 40k miles.
Bottom line:
Older than 2005.5, don't buy an automatic
Newer than 2005.5, buy only the DSG automatic or a manual
With all of the TDI's, take special care that the timing belt has been done within the specified interval (generally 60,000mi unless someone has used one of the more recent 100,000 mile kits) and has been done properly. If anyone has done a "mark and pray" method of timing belt change on these TDI's, they're very likely to have a piston hit a valve at some point. It's not hard to do it right, but it does take special tools.
All that said, my next car will be a 2010 or newer Jetta TDI Sportwagen with that DSG transmission in it
If only VW would offer the AWD version on this side of the pond...
BTW, here's a great diagram of the DSG automatics:
http://cars.about.com/od/thingsyoun...ronic-transmiss/VW-Audi-DSG-diagram-large.htm
