There has been a lot of discussion on this issue, in numerous threads. Some people have taken this out of context and now believe you HAVE to have them. Before I start you should know that I am an advocate for heat sinks on the Raspberry Pi. BUT!!!
Knowledgeable Members of the Raspberry Pi Foundation and Design Team have stated they are not needed for the normal operation of the Raspberry Pi device! Some have stated you do not need them for any type of operation of the Raspberry Pi.
So how should you read into this? You shouldn't. If you are using your RasPi within the normal use the foundation foresaw for the device YOU DO NOT NEED Heat Sinks for your RasPi. The BCM2835 was designed to operate within a closed case without any problems.
It is others, and my opinion, that a Raspberry Pi used outside of the foundations "normal" use MAY benefit from heat sinks. Not Need Them, but MAY benefit. Outside "normal use" I will define as Use in a CarPC, A closed case that incorporates other heat generating equipment etc..
Of course if you just want to dress up your RasPi for a trip out on the town or a local Raspberry Jam, Then you are more than welcome to do that with heat sinks. The heat sinks will not hurt it either. It comes down to the fact that you do not need to waste your money on heat sinks! As @AndrewS has stated some of those who believe in using heat sinks are old overclockers that believe every chip has to have a heat sink on it. And he may be right. It cost me $2.25 to put them on mine. (actually it cost me $20 for 10 big ones and 10 small ones plus shipping)
