Is it harmfull for my computer to be a Supernode?
No. Being a Supernode helps other users. Other computers connect to you, and your computer does the searching for them. Your Supernode communicates with other Supernodes worldwide to help other members search the network. The amount of CPU resources that can be used by a Supernode is limited to 10% of the total CPU power available – you will in general not even notice if your computer is functioning as a Supernode!