What is the significance of "Zealot" in Acts 1:13? When they arrived, they went upstairs to the room where they were staying. Those present were Peter, John, James and Andrew; Philip and Thomas, Bartholomew and Matthew; James son of Alphaeus and Simon the Zealot, and Judas son of James. (Acts 1:13 NIV)


What is the significance of calling Simon "the Zealot?" Is this some proper Jewish title, or what?
From Wikipedia: http://en.wikipedia.org/wiki/Zealotry I'll quote an interesting part here.


  The Zealots objected to Roman rule and violently sought to eradicate it by 
  generally targeting Romans and Greeks. Zealots engaged in violence against 
  other Jews were called the Sicarii.[9] They raided Jewish habitations and 
  killed Jews they considered apostate and collaborators, while also urging 
  Jews to fight Romans and other Jews for the cause. Josephus paints a very 
  bleak picture of their activities as they instituted what he characterized 
  as a murderous "reign of terror" prior to the Jewish Temple's destruction.


This says A LOT about what Jesus was able to accomplish in assembling his 12.  Considering he had a tax collector, and a Zealot, who under other circumstances would target such a tax collector as a "collaborator".  Consider the teachings of Jesus, and imagine how much of a life change that this Simon had undergone.  Things like "Love your enemy", and "Give to Caesar what is Caesar's". It doesn't say that Simon was a Sicarii, but there were probably some shared core beliefs. 

I am not a Bible scholar, but I think Zealot means more then just being zealous for Jesus.  It is capitalized in the passage you shared.