Despite this assurance from Apple, I continue to get reports that deleting one of more of these OpenFolderList files eliminatesvarious problems. For example, in addition to more confirmation of the previously reported watch cursor problem, Udo Ludtke writes he kept getting a "files are open" error message when trying to optimize his disk with Norton's Speed Disk. Deleting the duplicate OpenFolderList files eliminated the problem.
As to what these files are supposed to do, an informed source concurs with previous reports that they keep track of information about window placement. The file on each volume stores information about that volume. The additional one in the startup disk's Preferences folder is for storing information about previously mounted non-writable volumes, such as CD-ROM discs.