I have been daily driving my 2008 STS since late 2011. Currently have 156k on the 3.6.
I had an ignition coil die at 90k, then again (same cylinder) at 148k. It does consume some oil, like a quart in between oil changes.
I replaced the passenger side motor mount due to vibration issues. I have the drivers side, just haven't found the time to get it in.
The alternator has been replaced, the power steering pump has been replaced, the water pump was replaced at like 45k miles due to a leak.
Inside the car I have replaced the blower motor twice, the blower motor resistor 3 times, the blend door actuator, and now it needs the other actuator replaced as I can hear it clicking and making noise. The driver side lumbar support stopped working. I opened it up and found the plastic gears were broken. I replaced them with ones I found at a junk yard and they lasted a couple weeks before breaking. Now it is disconnected.
I wouldn't consider anything I have done as major problems, just typical maintenance. I am actually in the market to get a full size SUV, but I can't justify spending the money because my STS still runs great!