I've heard that butterflies can be a sign that a loved one, who has passed away, is in your presence. My first thought when I saw it, was of my grandma who passed away from cancer in October 2007. It was a very difficult time as she meant the world to me. I still think of her often, and on that day of 'the butterfly' I felt that she was looking down on me at my home-away-from-home.
We still have distant relatives in Finland, whom I was very fortunate to have met when I made my first visit in 2002. Before my grandma got sick in 2006, I had 'convinced' her to make the trip with me to visit Finland. She didn't care much for flying (and it is a long journey to get there!) but she had decided it would be a great experience. I was very lucky to have traveled a lot with my grandma, mostly by car, but we did fly together once to Reno, and I dreamed of 'taking her' to Finland...
We never got the chance to take our trip to Finland together, but I thought of her often on my journey. Was this her way of saying "I'm here with you in spirit"? Maybe so, or maybe not, but either way I hold her in my heart, and her memory will always be with me.
Here is an interesting website that I came across: