Version: 2.0 (using 4.1.3 (KDE 4.1.3), Kubuntu packages)
OS: Linux (i686) release 2.6.27-9-generic
This is the same as Bug 127473, which was resolved in Amarok 1.x successfully, but is back in 2.x.
Amarok rescans your collection every time you unmount and remount your media while Amarok is running. For large collections (1TB in my case), this means hours and hours of scanning every time.
1.x handled it very well by just bringing back your collection without rescanning when it was remounted. It has since disappeared in 2.x.
*** This bug has been marked as a duplicate of bug 171213 ***