Here's a really dumb thing; have you blown the dust out of the space between the heatsink fins? I remember in college I could slowly see the temps rise a degree or so each month. Hell, the computer that built my brother would idle @ 28C and wtihin a few weeks of living in the dorms, he was already up to 31 idle; and thats after only a few weeks of use. I also saw the same thing happen to a friend of mine. His actually had so much dust in the heatsink that the computer would shut down to protect the chip.