It was signed into Law several months ago, about the only thing that could be done about it is an election were a new government was put into power with a majority, and they decided to change the law.
The likelihood of any new government changing the tax laws at this point would be political suicide.
The PST division is already well under way of being totally dismantled - all of the employees have been issued their severance cheques (even though they have been moved to the HST devision). New contracts would have to be drawn up, and severance payments would again have to be paid out to move those same employees from the HST back to a newly established PST. Also no government is going to give up tax money so easily.
Think back to Mike Harris, when he won the election by basically promising to get rid of the perceived tax grab that was Photo Radar.
We no longer have photo radar, but in order to pay for things and balance a budget we also non longer own the 407, among other things.
I vote every election, but I am a firm believer that we are damned if we do and damned if we don't. Politicians don't run the government, bureaucrats do... and they are not elected and don't change because of an election.