I'm a self professed audiophile. Bluetooth audio is fine for "regular" speakers and audio systems. You won't notice any difference due to the fact that they actual audio system lacks the ability to play at a level where the differences are discernable.
If you have a pretty good system then you can DEFINITELY notice the difference. I have a zuneHD, Kenwood KIV-700 (with the external Bluetooth kit), and about $4,000 worth of high-end speakers and amps in my car (huge note that I'm not a basshead at all), and I can hear the difference between the zune playing through the dock vs the headphone jack. It's night and day. Bluetooth is technically a step below that, because it lacks the frequency range required to transmit the lowest and highest notes. This has been solved with Bluetooth 4.0, I believe, because they focused on improving the sound quality. Yes, the One X has Bluetooth 4.0, but the other side of the connection also has to have it. I haven't seen any aftermarket radios with anything higher than 2.1 + EDR, let alone factory radios.
TL;DR factory systems and basic aftermarket systems will be fine with bluetooth audio. Audiophile types with higher end systems will want a USB connection at least. This is also assuming that the radio can read the MTP protocol, which I don't think any do (but I also haven't specifically checked).