In Sweden I think they got the support they did for a number of reasons.
1) The Pirate Party got the votes in the EU elections, not the national one. The Swedish national elections are coming up too and they don't even show up in the polls yet (meaning they have less than one percent). Basically, it seems like people in Sweden do not care about the EU elections that much, or alternatively they believe copyright is a European issue and not a national one.
2)There is a history of personal freedom where people believe that private citizens should not be monitored unless deemed absolutely necessary for criminal reasons. In the span of a few month, ThePirateBay was sued and in the media it appeared to be a result of pressure from the US. Also, ThePirateBay's servers were seized together with the servers of a number of companies, who made the only "mistake" of putting their servers next to thepiratebay's servers, most likely this was done unknowingly. Furthermore, laws were being discussed that would further reduce personal freedom and allow mass monitoring of the population. Stories were written in media and people got annoyed and began loosing trust in the authorities which resulted in more votes for the PP. Basically, they got votes from unhappy people.
If current polls are an indication, the PP is unlikely to have any impact on the national elections in Sweden. Instead, Sweden is jumping on the European extreme-right bandwagon.
We were unhappy with copyright laws, now we are unhappy with immigrants. My current prediction is that in 2014, we will have anti-dolphin parties (dolphins creep me out).