In Windows XP, while a font was open in the font previewer you could also use it in other applications. It was kind of like a temporary install of the font. When you closed the previewer, the font would no longer be available. I used this feature often, as I have a lot of fonts I want to use only for a short period without having them clutter up my font list.
This doesn't appear to be working in Windows 7. Is this a feature that Microsoft eliminated?