I'd have to say it's good luck and nothing to fear.
It rained on our wedding day (30 June 2004) while I was on my way from the changing room to the chapel....then when we came out the sun was shining really bright (and in Scotland too if you can believe that!!!) we took all of our outdoor pictures and as we were on our way back to the hotel for our reception it was pouring down rain.
So honestly, I don't see it as too much of a bad thing.
x x x