The theme for my son's 3rd birthday was his favorite color, yellow. I had found a picture of a beehive cake, where the bottom layer was a 10 inch round layer, topped with an 8 inch round layer, then a rounded top baked in a large 8 cup glass measuring cup. The original recipe called for tinting a can of vanilla store bought frosting yellow then microwaving it for 30 seconds, then pouring it over your assembled hive to coat it. I don't like the taste of store bought frosting, so I made the vanilla butter cream from the CMD books, colored it, microwaved it for 30 seconds and poured it over the cake. I put wooden bees on it for decoration. It came out absolutely adorable.
I wasn't sure the home made frosting would give the same consistency, but it came out great. In fact, it sort of formed a firm covering - not hard like a shell, but definately hard enough not to stick to plastic wrap. I had to scrape up the drippings, melt them again and cover the cake about 4 times because I chose to make the cake a chocolate cream cheese pound cake, so it took that many coatings to cover the darkness of the chocolate.
Thought this might be useful info. in case anyone hadn't given this a try.