May be the same issue as in earlier thread but here's the numbers.
Just updated to 6.0.1367, no other changes to setup. (with 120201-0 defns) under XP.
Scan speed plumeted down; found that . . .
scan of C: with normal mix of files, speed = 80 MB per sec (Disc access bound)
scan speed of folders with mp3 files,speed = 1.2 MB per sec. (Processor access bound)
Full scan of machine changes from 3 hours to (estimated) 100 hours.
Any clues?