Due to a family situation, I've been unable to read or post as much as I'd like recently. So, my thoughts on the Spanish election are based entirely on my own gut instinct.
I presume that the swing from the PP to the Socialists was more due to the government's untruthfulness rather than the bombings themselves. If the government had hedged its bets more, I think the voters may have been more willing to vote as they had intended according to the polls before the bombing. But, the government, particularly the Minister for the Interior, was so adamant that it was ETA that when that turned out to be false, the people reacted accordingly. I, too, was revolted by this and may have voted for the Socialists in anger if I were Spanish.
The attempt at misleading the public by the Spanish government was far more serious than the inaccuracies of the Bush & Blair governments in the run-up to the war in Iraq.