Nope,they aint accurate atall. I would guess that the acctuall sensor and electronicsmay be accurate to +-3c.
Then I would add, look at the positioning of it. BELOW the cpu. Any heat has to travel through the cpu package to get to the sensor. The package has a fairly high thermal resistance = not all of the heat goes through = you get a much lower reading.
THEN when installing the cpu, how many of you put paste on the sensor,and bend it upwards to get better contact?nope, I dont either.
THERE is however, a simpler way. If you can solder small simple circuits, then its also almost free. www.maxim-ic.com
look at MAX6657. You should be able to get free samples too - I did.
This then gets a measurement from a sensor internal to the cpu, which needs no calibrating, and is in perfect place for temp measurement. Theres almost no thermal resistance and so very sudden changes in temp are noticable instantly.
I b0rked all my samples, however I may try again, Ill post in the electronics forum, if anyones interested in following this.