The new (mid-2010) Mac mini now streams high-quality wireless audio thanks to a professional-grade audio coding technology called apt-X. Apt-X worked directly with Apple to implement, tune, and optimize the Bluetooth for ideal stereo experience.
apt-X facilitates the real-time transmission of full-bandwidth audio (20Hz to 20kHz) over Bluetooth A2DP -- that's the advanced stereo/speakers/headphones profile, not the simple mono/phone/headset profile.
To appreciate the noticeably higher fidelity Bluetooth in latest Mac mini you have to use apt-X compatible Bluetooth headphones (Sennheiser PX210BT, PXC310BT, PXC360BT; JayBird Sportsband SB2; etc), Bluetooth speakers (Creative Inspire S2 Wireless, ZiiSound D5, etc), or Bluetooth line-out adapters (QED uPlay; JayBird uSport; Chord Chordette GEM, PEACH; etc).
More apt-X enabled Bluetooth products from other trusted CE brands are coming to market this year and next. Some other apt-X clients include JayBird Sports Audio (check out the apt-X Audio Demo widget in the left sidebar) and several other partners, including Sennheiser and Creative.