My Raspberry Pi has reached without cooling in a plexiglass case after 2 days of continuous operation approximately 52 ° C (idle). Under load it went to just 62 ° C. Without overclocking (700MHz). With heatsink and at overclocking the Raspberry PI (Turbo, 1GHz) to reach the Idle after 2 days of continuous use about 48 ° C (Idle) and 59 ° C under load (apache2 / ownCloud server). This is the deep green area (CPU max ~ 85 ° C). Am however not sure if it would ultimately have been "really" necessary. My conclusion is that I can now the CPU Overclocked run at the same temperatures as without. And so far no crashes or other abnormalities. For the price definitely worth a try.
