Revit's Annotations, Tags, Titleblocks, Schedules, Dimensions, and Text Tool are all setup to Arial by default and there is no one place in Revit to change Font styles and sizes so, like linestyles, you have to kind of search around to find all of them. We use Times New Roman in our office so I had to change the fonts in our template one at a time. Hopefully sharing my experience will help you.
Annotations, Tags and Titleblocks are family files. In your project browser go to Families... Annotation symbols. Here you can right click on any of the loaded families and EDIT them. Once you have the family open just select the text label and go to its properties. Click on Edit/New to change its type parameters. It is then a simple matter of reloading the annotations back into your template file for use in all projects. If you choose to rename your tags you'll have to search around in Settings... Annotations or Settings... View Tags to apply the new families to your template.
Revit's Schedules will, unfortunately, always default to Arial, so you'll have to do the following everytime you create a new schedule. While in the schedule go to View Properties (VP). The fonts are configured under Appearance. (Note: In Revit 9 you can now save a schedule's formatting for use in other projects... While in the project browser right click on the schedule and Save to New File)
Dimensions and Text are fairly simple to change. While in the Dimensions or Text tool just click on the Properties Icon and go to Edit/New. Now you can change the fonts for all your dimension types and all your text types.
If you want to purge unwanted Text or Dimension Styles go to File... Purge Unused... Check None. Then check the objects you want purged from the template. It is important to be aware that the only objects that show up on the purge list are objects that are not currently in use.