I noticed that repairing permissions on a new Leopard install led to THOUSANDS of repairs on language localizations (in .app contents). It eventually finished.
Initially my Tiger install also had something sucking all it's cpu time. Activity monitor said processes "mds" and "mdimport" were my culprits. Search of Apple came up with one spotlight related page. Two days later my cpu is back to twiddling its thumbs waiting for me again--looks like...