Pew research center has written an interesting report on the twitter activity leading up to the EU elections. Not surprisingly, the British right wing anti-EU party UKIP received more attention than any other political party. The Pew article didn't mention it, but I think the enormous attention on UKIP was partly due to the hashtag #WhyImVotingUKIP, which developed into a parody tag, and trended for days.
I'm not going to summarize the article here, as it's short enough to read in a few minutes. It's worth perusing, though. Twitter has played a major role in world events for the past few years, and it's encouraging that Pew Research is taking social media's role in international politics seriously.