Hello,
as you know "need is mother of inventions" and this is my need:
I have 60 gb hard drive full of mp3s which travels with me to almost every party.  But whenever i plug it [its USB] i have to rescan whole collection [i tried moving ~/.kde/share/apps/amarok but its too big ingerention in someone else's system]. What i need is an option to plug my disk, scan it, write a DB to it as a file and on the other machine show amarok this file saying, "from this catalog, recursively down use this file as DB, merge it with local DB but use it only for this session becouse this files are there only temporary"

check out the dynamic collections stuff in 1.4.2 and latest svn.. it should be what you need