Although Google fonts are helpful to create a good graphical layout, the need for user browsers to pick them up on demand from Google creates a potential privacy issue. Through the fonts API, Google gains another potential method of tracking people as they visit a site using Google fonts. The only way to prevent that is to download the fonts and offer them via the "traditional" font kit method, but I'm not sure that is allowed under their license.
Thus, beware. Here too, "free" isn't. If you're in Europe, you could unwittingly end up with issues under EU Data Protection laws. It's a shame, this plugin is really helpful..