As soon as you open a file, you should get a message that tells you if any fonts are missing and which ones they are.
Font missing dialog box on opening.
There also should be an option to embed the fonts into the file, so you don't have to reinstall them whenever you open it on another computer :3
Perhaps not a forced dialog box, as any dialog box that pops up on opening a presentation is inhibitive to work flow. Given modern design, perhaps a message in the yellow information bar that can appear below the ribbon for messages (eg when an Office Update is available), with a button to then display a dialog box listing the fonts.
Better yet, this should be a FONTS REPLACEMENT dialog box - I think OpenOffice Impress has this feature?
This would make it much easier for people to understand why their presentation looks 'wrong'. Such a frequent issue these days with everyone wanting to differentiate themselves by using non standard fonts.
Lesley Ross commented
This would save sooooo much time. Please do this.
Robert Stone commented
Also a dialogue box to tell you which fonts are being used on which page and an easy way of deleting unused fonts (single & double byte). + The same listing for multimedia files