I just bought a couple digi thermo's and tested them with my tap water. My previous thermo read 56 degrees and the two I just tried read no more than .5 degree off. I should add my previous thermo was the 40 dollar waterproof kind from Professionalequipment.com so it was about as accurate as you can expect. I think people worry too much about this stuff sometimes especially since the temps can vary a couple degrees in your mash depending on where you take the reading.
On Tap: Hobgoblin, Coffee Stout
Bottled: Arrogant Bastard clone, Summit IPA, Apfelwein