Thanks to my mutually-reinforcing compulsions for baking and kitchen equipment, these were put together in no time -- a basic creaming method. Both of the frostings were surprisingly creamy, although to be honest I have no recollection of what the fluffy vanilla frosting tasted like. The chocolate frosting, however, was really tasty and less melty than other non-vegan chocolate buttercream frostings I've made. Piping this stuff was probably the most fun part of the process, but I'm going to need some better decorating tips.
The only vegan cake I've ever enjoyed was the Chocolate Vegan Death Cake that I've made about a dozen times the past couple of years, and it looks like it's a formula worth exploring. Margarine, however, is strange and nasty stuff. I'm much more accustomed to butter, and the slightly metallic taste of the margarine/shortening fat combination was a little off-putting. Overall I give the vanilla+vanilla combination 5 out of 10 Ani DiFranco songs, and the vanilla+chocolate combination gets 7 out of 10 hemp necklaces. The basic cupcake was, as advertised, functional but a little too birthday-cake-y for me. The vanilla+chocolate had a lot more character, mostly due to the depth of the cocoa flavor in the frosting. And yes, I plan to rate each of the cupcakes I make on an appropriately vegan scale from 0 to 10. Here's a really ugly picture of the vanilla on vanilla: