I'll just keep it short and sweet:

Running 8.10, all the updates.
Two SATA drives. For no apparent reason, when trying to copy files to the one I use as a backup drive, the file transfer has turned slow, around 1.3MB/sec.
Nothing changed here. Both ext3. Drives have been checked and rechecked. No errors. Cables on hardware secure. Plenty of free space left on each one. Bios settings are good. Seems like I've checked all the obvious.

Open to ideas.. ..