I jumped back onto the VW forums to look around to see what problems have developed, here they are....
Intake manifold: it's a composite piece and there's a valve that fails on the 2010 and 2011 models that causes the car to run poorly. This seems to be, perhaps, the most common issue you can encounter. However, VW updated the part for 2012 and you shouldn't see any more issues. The part is also relatively cheap, like about $150 and apparently isn't too difficult to replace.
Throwout bearing: there's a TSB for this one. On some cars it howls and makes noise, particularly when engaging the clutch from a stop. My car does this infrequently, maybe once every few weeks, except when the temps are below freezing and it does it all the time. The way to test this in a used car is to engage the parking brake and attempt to get the car rolling, if it's bad enough to take to the dealership for repair it'll make the noise. The dealership shouldn't hassle you about warranty repair on a normal wear and tear item since there's a TSB out on this; could take advantage of the free labor to get a new clutch installed at the same time. There are no known total failures related to this that I could find, just noise.
Fuel injectors: this one is extremely rare, and seems to occur very early in the car's life, but every now and then they go. Again, not common, nothing to worry about (IMO).
Water pump: this one is kind of a turd-shoot. It seems to be somewhat common, but VW also updated this part so if you get a newer GTI you shouldn't have issues. If you're buying used, on the 2010 and 2011 models if the water pump was going to go bad it has probably been replaced by now.
Intake valves: carbon build-up. Not as bad as MkV GTIs, but it still happens. Expect to want to dig in and clean this up at about 100k miles.
Timing chain tensioner: this seems to be the biggest boogieman worry about because it can cause the greatest amount of damage. That said, I really don't feel that this affects a high percentage of cars, and seems to be quite rare. It also seems that VW updated this part by adding a ratcheting function that prevents failure from causing a loss of timing extreme enough to bend valves.
Knowing this I'd still buy one. The only adjustment is that I intend to add the following items to my 100k mile service...
Clean intake valves
Replace intake manifold (fairly cheap, have to remove the old one to get to the valves anyway)
Water pump
Timing chain tensioner
Doing all that myself may add a few hundred bucks and an afternoon to the ownership cost of the car. Paying an independent VW shop to do it.... maybe $1000 to $1500 in parts and labor, still not too bad for a car that drives as nicely as the GTI does.
Also, for driving enthusiasts who care, on the 2010 and 2011 models you can now disable ESP via VCDS by turning off the steering angle sensor.
I hope that was thorough enough, but not enough to freak anybody out. Every car has some acute issues, but I feel that these are all manageable and don't really remove the car from the "reliable" category. However, I might change my tune if my timing belt tensioner fails on me....
