I made this buttercream to go on lemon cupcakes and it was absolutely perfect. I did modify the recipe a bit though. Rather than using all the vanilla, I used 3/4 tsp vanilla and 1/4 tsp lemon extract. I didn't use quite as much powdered sugar as mentioned and also added a few blackberries right before I frosted the cupcakes to have larger chunks in the frosting.
very good icing!! everyone loved how unique the flavors were. Perfectly sweet, but with the kick and tartness of a blackberry. the only drawback I could find was that some people didn't care for the tiny blackberry seeds that are in the icing.