Guidelines for using fonts in templates

I’m setting out to design a new template, and I was wondering what you do when it comes to fonts.

I’d like to use some premium fonts for my demo content (via TypeKit), but that would mean either including a common font (e.g., Helvetica) or using something like Google Fonts in the actual source files when the template is downloaded.

So my question is this: what do you do when it comes to fonts?