Hours, days and even the tentation to buy an expensive plugin which is 10 times more BASIC than this one and then.. I found this.
This plugin is Freakking AMAZING, 10 starts, it just works, no matter the theme you're using, it just works! I never found anything this simple to use, the author should be commended for this, it even works on the latest WP 3.6, not a single problem.
My countless hours trying google webfonts manually are gone, this plugin let me see REALTIME how my website looks with new fonts, something that is simply invaluable.
If the author wants, I could do a complete review in our labs website.