no offence to developers but those themes lag and are not properly tested in all aspects , i tried blue sky but it just looks ugly even after restart.... black plastic afaik is a combination of 1 theme with different colours while it might be a good idea i dont think it works well + custom transitions are worse then original

also keep in mind that its not entirely their fault our "beloved" Nokia maemo team screwed up hildon desktop components with PR 1.2 , a lot of people including me had issues with theme changing , freezes and crashes of hildon home