I believe that the OnyX Reset function as described in OnyX help:

"Links between documents and applications: OnyX allows you to delete the files which store the links between documents and applications, as in the rebuilding the Desktop under Mac OS 9. When you launch a new type of document for the first time, an alert message appears. You can open the application choosen by the system, display this application in the Finder or cancel the opening document. When opened, the link between this document and the application executed is stored in a file located in the /Library/Caches/ folder, as every account has its own file."...

has causes a dire problem on my machine and it's many QuarkXpress files. In Quark there is a function that allows you to double-click a picture file and open it with it's native application (i.e.. Photoshop, Illustrator, etc.). After running this function in OnyX (reset) all of my Quark image files no longer can idenify their creator - they show as being linked the Usage window but their creator show "?" and will not open with a double click. The only solution that I have found to repair this is to unlink all the picture files and to manually relink. With many 200+ page catalogs with 1000s of pics this is a bit of a pain.

I emailed a detailed overview of this problem with screenshots to the developer and two weeks later got a reply that he can't read English (French).

I wouldn't use it again for a million bucks.