it's not that it isn't accurate, but more of 'it likes some MoBo's/CPU's better than others' Mine is fine and gives more accurate temps for my setup than Everest and PC Wizard did, so it's all a matter of trying them all, comparing the temps with each other and BIOS, then finding the one that works best.
Also, sometimes it takes a few days for SpeedFan to recognize all the sensors. I've installed it before on a system and it recognized only the CPU or HDD and one Fan. When I went back the next week, it saw both HDD's, Chipset, and both Fans. Not sure why it does that.