I got one of the launch late 2008 model unibody macbook pro's and am suffering the same issue as you are.
Symptoms: excessive and uncomfortable heat coming from hing area. DRASTICALLY reduced battery life as a result of excess heat.
When: The system does not have to be under load, but there are certain activities that really aggravate it. With a fresh install and with iTunes launched I turn on the "stix" stock visualization in windowed mode and leave the audio paused. The temperature will skyrocket in just a few minutes.
Attempted fix: I've brought my macbook pro in for repair several times. Each time they run a diagnostic stress test and tell me that it passed all tests. They replaced my left and right fans but it really hasn't done anything for my temperature spikes.
Thoughts: One of the early OS patches that was released addressed an issue that the U-MBP had waking up from sleep randomly. I often have my U-MBP in a neoprene sleeve in a laptop bag so there was more than one occasion that it woke up with no way to ventilate itself. My fear is that during one of those incidents some damage was suffered. Not a damage that results in outward uncorrected errors, but perhaps one that causes more internal CPU resistance and higher running temperatures?
I can't say for sure, but I plan on bringing my machine back in and insisting on a motherboard replacement because this level of heat/battery life is really not normal.