I have owned for 2 years and put 55K miles on my A3 TDI. Bought car for performance and great MPG - commute is 100 miles per day. With 500 miles left on warranty Mechatronics unit went - first time had issues was 25K miles and dealer did software update. (it's roughly$3,200 repair if out of warranty). At 54K miles EGR valve clogged with ash - ($800 repair & AUDI offered no help) I called AudiUSA and got nowhere. DO NOT BUY this car for MPG savings, you'll give it all back in repairs. Overall nice car but, I also own 2 Toyotas and I'm spoiled by the fact that they don't break...I had always heard that Audi/VW reliability issues were a problem, definitely some buyer's remorse on A3
I'm coming from the perspective of a family with young kids that has relied on Outbacks and older Nissan/Acura sedans. Our newish Outback serves as our workhorse car, so we felt more free to replace our aging 2nd car with a smaller non-all wheel drive car. We've been very happy with the handling and performance of the A3. I've gone through NE winters with front wheel drive and snow tires, and expect the A3 to do just fine. It feels plenty fast to us, and the handling and responsiveness is a clear cut above what we'd been used to. My wife was a bit hesitant about it after the first test drive, not being used to a diesel engine, but now even she says it's the perfect car for us.
In most categories, I love this car. I like the look, the fuel economy, it's fun to drive and has a great stereo. The turbo lag does take some getting used to - When accelerating from a stop, it can take a full second or two for the turbo to engage. It's very responsive once you've started moving. Fuel economy is great and overall, it's really a fun little car. However, you should be aware that the heated seats are basically useless. My dealer explained that they have heard numerous complaints about them and that they perform 'to Spec'. If you Google Audi Heated seats, you'll find several Audi forums discussing the issue. If you love heated seats like I do, know that they don't work.
I recently bought an A3 TDI and have enjoyed the first 2k miles. 35 mpg with fairly aggressive mixed city/hwy driving. I like not having to baby it to get good mileage. The car is very stable and composed at highway speeds and in the daily S. Florida rainstorms. If you test drive it, look for two things. 1) Diesel motor tick. It has such a quiet cabin that you may not hear it in a test drive. You'll hear it in your driveway though. Make sure it is not an issue for you. 2) Its truly an automated manual transmission it "catches" when coming to a slow stop, just like a manual does. Those not used to manuals may not like the feel. I love it though and am very happy with the purchase.