CSS Changes Never Apply
Under vBulletin 3, if you make changes to the wiki CSS, you may never see the changes, nor will your users. vBulletin 3 has no internal identifier that lets us know the style cache has expired.
Fixed in the next release. Since vBulletin 3 has this design flaw, we now force users' browsers to ignore the cached CSS every 15 minutes. This will increase server load, but at least it will allow updates to apply.
If you are making changes and cannot wait 15 minutes for the cache to clear automatically, manually clear your browser's file cache, or disable it completely.