I'm about to pull the trigger on some way too expensive bluetooth headphones, and during my research I came across these two articles that are worth a read if you care about bluetooth audio:
Headphones or earbuds that support the latest bluetooth audio options link the volume changes made on the headphones and computer/phone, will show a battery indicator on your iPhone, can do calls using reasonable audio quality (16 kHz, old ones use creaky phone quality at 8 kHz).
And last but not least, can accept AAC audio. With that, there's no difference in quality between wired and wireless playback of AAC-encoded music such as iTunes+ songs. Unfortunately, only a few headphones support AAC over bluetooth, and many don't bother to mention this on their website... (You can check on your Mac by alt/option-clicking the bluetooth icon in the menu bar.)