Autodesk announces release of Mudbox 2012 Service Pack 3, which is possible to download on Autodesk web page. It includes all improvements from others service packs released before and some additional. It addresses quality issues when re-importing PSD files into Mudbox and also in release notes you can find best practises when exporting to PSD and reimporting.
This service pack you can download here: Autodesk
Release notes: Mudbox Service Pack 3