Losing Subscripts in Google Docs when exporting to PowerPoint

The problem here is not google-docs export of the file, it's the fonts Power Point is using to display the file. A "blank box" like you describe is the standard windows response when the font it's asked to use doesn't have the character you asked it to render. Some apps will detect that and automatically switch fonts to one that does, I'm pretty sure Power Point is not one of them. I've seen similar behavior in the past and just taking the same .ppt file to a different system that had better fonts installed, or a different application that did a better job of picking a font solved it.

This is currently not a Google Docs feature (and not possible) based on online documentation and no better answer. Apparently, this worked at one point in Google Docs, but it required viewers to use Google Talk (and this combination was buggy at the time).

An alternative I went with is PowerPoint 2010, which comes with a feature to broadcast slideshows to users over the Internet.