Other threads have discussed the TuneIn issues, which I have experienced, but so far my Slacker has been OK.
USB is usually OK, but the media system has always -- to the best of my recollection -- occasionally switched sources when the car is parked. I'll be playing the USB, park the car, and find come back to find some random FM station playing. Fortunately that happens only once a month or so.
Keeping my fingers crossed that Slacker is OK for me when I use the car next time!