Analogs have other drugs in them the contribute to the high that you get from smoking them, and also contribute to the addiction. Nicotine itself is not a chemically addictive substance.
Because e-cigs lack these other drugs and only contain nicotine, most people end up using much higher doses of nicotine then they should because they're trying to get the same feeling as smoking an analog.
However, since their intake of nicotine is now much higher then it was when they were smoking analogs, they are experiencing more of the negative side-effects associated with nicotine and stimulants, such as hyperness, grinding teeth, anxiety, short temper, etc.
E-cigs have a long way to go before they start accurately replicating all of the effects that you normally get from an analog high, and until then, people will continue using more nicotine then they normally would (if smoking analogs) because they're trying to replicate that feeling, so they will also continue to experience the negative effects.
Outofstep: That is some interesting information. If PG is 1/3 the potency of ethanol, then that means the PG is nearly as potent as 80 proof liquor like vodka, rum, etc.