The problem with installing the font on your Mac is that, if you mess up the code and publish to the server, the font will still appear OK in your browser. To test it properly you need to uninstall the font from your Mac.
Since I am using widgets to set the font family, I don't have to install the font on my Mac and don't have that problem.
 If you want to install a Google hosted font and self host it, you cannot install it on your Mac and use the Fonts window to select it. If you do this, EverWeb [V1.7 and 1.8beta] will insert the link to the Google hosted font which kind of defeats the purpose of self hosting it.