The problem: Font substitution is a particular problem in cross-platform deployment, although by no means limited to those settings. Arial and Verdana both have 99% penetration on both OS X and Windows, but for virtually any other font, penetration drops off for one or both platforms. Throw iOS and WebDirect into the mix, and things get even dicier.
The proposal: To ensure better control over the look of our layouts across different clients, therefore, it would be great to be able to specify a font fallback stack with our custom themes. Given that CSS supports font stacks as part of its font-family property—and given that we’re cautioned, of course, against going in and editing the raw CSS of themes—the solution would seem to be to expose this formatting capability in the Inspector. I’d argue in favor of specifying it a theme’s root level, so that we wouldn’t need to do this for every different layout object type. That would help ensure consistent typography across a solution, and make it easier to make solution-wide changes.