After upgrading my home system to Tiger, I noticed that my RsyncX backups to an external FireWire drive were no longer working. Much consternation and hair-pulling later, I realized that the Spotlight indexing was causing problems with RsyncX. I used mdutil to disable indexing on that drive, and the problem was solved.
Ed. Note: keep in mind that Spotlight indexing can make any type of file transfer take longer due to the overhead of indexing every file. This is especially true when you’re moving large amounts of small files.