Politifact and FactCheck.org can be very useful if you actually read what they write, and use your knowledge, in context, to add to your understanding of the facts surrounding what candidates say. But I've found their top line true vs. false judgments to be puzzling or even comical in the way they seem to ignore the substance and intent of the utterances they're rating.
Sometimes it's as if a candidate were to tell a midwest audience "I spoke in Boston yesterday," and one of these factcheck orgnizations rated it a lie, explaining "she had an event in Cambridge, MA, yesterday, but never set foot in the nearby city of Boston."
Here's an example of what I mean, from last night's debate. When Obama said "the essence of [Romney & Ryan's] plan is that he would turn Medicare into a voucher program. It's called premium support, but it's understood to be a voucher program." - factcheck.org tweeted:
Obama says Romney-Ryan Medicare plan a "voucher" plan. Not exactly. http://ow.ly/ecMAl
... and linked to this already-written article on Obama's stump speech in which they address the "voucher" matter:
He attacks Romney's plan for Medicare as a "voucher" system that would leave seniors "at the mercy of insurance companies," when the fact is, it's structured the same as the system Obama's health care law sets up for subsidizing private insurance for persons under age 65.
Technically correct - the best kind of correct! That could be their slogan.
Yes, as I've actually written in other places, a good way to sum up Ryan's plan for Medicare is that he wants to turn it into something very much like Obamacare* - which is indeed equivalent to a voucher system. But while that's a major upgrade for people under retirement age, who pre-Obamacare get much less than this, it'd be a severe downgrade for people currently on Medicare, who currently get guaranteed - and good - insurance. Factcheck's implication that Ryan's just trying to do the same thing Obama already did is bizarre considering that key difference.
But back to truth-rating Obama's statement: Obama said "It's called premium support, but it's understood to be a voucher program" - and that is exactly correct. Amusingly, Politifact had previously explained all of this and ruled that it is reasonable to call Ryan's system "vouchers". Although they rated it "mostly true" to simply call it a voucher system, because it's a slightly different kind of voucher called "premium support" that has some features not all vouchers had ... Obama in the debate said directly that it's "premium support" and that's essentially a kind of voucher system. He was 100% correct, no qualifiers, in this case.
So, do make heavy use of Politifact and FactCheck.org to understand the facts behind what candidates say. But don't be misled by their ratings or take them at face value; read, analyze, and come to your own conclusions.