The rhetoric of violence is not the only kind of rhetoric that encourages violence. The apocalyptic rhetoric we've seen from some on the right, most notably Glenn Beck, should be part of this discussion too. When Beck portrays Barack Obama as the head of a socialist/communist/Nazi conspiracy whose goal is the literal destruction of America, he is implicitly encouraging violence. If that really were the nature of the administration, and our liberty really were on the verge of being snuffed out, violence would be justified.
The apocalyptic rhetoric is what we really should be talking about. The flat-out making stuff up and feeding it to the masses 24/7 just to fuel and build the hate. I think it dwarfs the "violent rhetoric".
This type of rhetoric has always been around but I think its reached a dangerous level in the last few years. I thought the left took it too far with the "Bush stole the election" talk but the right has gone off-the-charts since the the Obama win. Limbaugh, the Fox crew, talk radio, Palin, Bachmann are all guilty of this rabble-rousing. They're all trying to out-crazy the each other.
I thought there might be a lull after the Arizona shooting, and there might have been if the shooter had ties to one side or the other, but it looks like he was just an independent nutcase so both sides are ramping it up trying to put him in the other guy's camp.