I have a dozen Macs for my designers and artists. I've recently noticed something odd. Helvetica Medium will occasionally cut class. Everything will be fine for some time, then BOOM, files like Illustrator EPS with the font will begin to tell us that the font is missing, though noting I can see has changed. The issue will be a thorn in my side (as well as the user), then will magically fix itself days later. I've repaired permissions, updated the OS and Adobe CS3, even replaced the fonts with an identical set from an identical Mac that has no issues. I've also cleaned the font caches manually: as well as with Font Nuke. Primarily, I've seen this issue with Macs running 10.4.11, but recently I've seen a few 10.5.8 Macs do it as well. It doesn't happen often, but it kills me when it does. I had thought it could be a conflict, but most of my Macs have not had this issue at all.