I was just trying to assert if the user knew exactly what he was using, because he had to get it somewhere. Let's say something dodgy or old grabbed on a free fonts site, an older TTF Linotype Roman, a something recent as later OT Std from Adobe that might have minor further adjustments. I just used Linotype as a random example.
This coupled with the way font rendering differs from program to program, not only at different sizes, but at zoom levels can sometimes be a major headache (not to mention different display panel technology vs sub-pixel). If the user tries to visualize that Powerpoint presentation in fullscreen, the problem might simply vanish.
The problem is the he's neither using programs made for publishing, or using a proper font designed as trouble free for screen use. But trying another provider for that font might solve the issue.