Minecraft wiki entry for Cake, associated text: Because cake is only 7⁄8 blocks wide, it is possible to stand on the edge of a block beneath a cake.
It is possible to place cake on top of another cake by placing a cake on the ground, then placing another cake on the side of a block above and to the side of the first cake, similar to placing torches on a chest. Eating the lower cake causes the upper cake to disappear, the same as mining out the block of cake it is sitting on.
It is also possible to place cakes (or any other block) on top of cakes by sneaking and placing a cake on top of another cake.
Mobs on top rotate while attempting to move, a pathfinding oversight shared with fences.
If cake is placed in a hole one block deep, players can get across the hole without jumping, although a player standing on the cake must jump to get out of the hole.
Cake can be used to create a functioning staircase, by placing a cake on each level of a 1 block by 1 block incline. This would be one of the most labor-intensive staircases available, given the requirements to craft a cake, compared to any other method of creating a staircase. This staircase is also extremely overpowered when combined with a horse being one of the fastest forms of travel.