I have ran a sony head unit in my last install, cant remember the model number but it was a mid level unit, i loved it and in fact am planning to use the MEX-BT500 in my next install partly due to the Sony 10disc changer I already have which i really like.
I have read alot of reviews on this unit and the only main complaint i have seen is that the BT feature is not so great, most users have stated that if the unit is down low in the dash, its really difficult for the person on the other to hear you due to the different factors of road noise, unit being installed low in the dash, etc. Also the microphone for the BT is behind the faceplace, go figure.
if i dont go with this unit i will definately be going with a different sony head unit, personally i feel the EQ is the heart of the system, all you need is a basic head unit to play a CD and then a high quality EQ to define the soundstage.
just my two cents, i vouch for sony head units, the subs and amps....well.....yuck! i wouldnt mess with any of that if someone paid me