I thought about the Holy Lance as a prop for a knightish kind of char too. For me it's just a neat way to keep in line with the Novels (
Having all three knights up an running if me and my group choos to set the time to an early frame of the storry would be cool!
).
A member of my group thought of the Lance as a weapon of evil too, but honestly that never crossed my mind. After some research I can see why you might get this impression though. For a long time the lance was owned by german kings and was used as a base of their royality. It was rumored that an army carrying the Lance in front of it could not be defeated. When Hitler and the Nazis came along they tryed to incorporate the lance into their propaganda (I know ... sounds just like "Raiders of the lost Ark"). So it's kind of tainted by them.
Longinus testified that Jesus was realy Gods son and converted to Christianity after the crucifixion. At some point he was declared a saint.
If you read the below linked wiki you will come across the Gospel of Nicodemus where Longinus name can be found ... that adds a little twist, dosn't it?)
Over the years several copys were made of the relique. Who knows where the Lance has ended up and to what purpuse it might be used.
For those who want wo learn more. There is a very nice Wikipedia article about the Holy Lance:
http://en.wikipedia.org/wiki/Holy_Lance