Why you made it - I saw examples of "knitting graffiti" online and was enamored with the idea of a relatively inoffensive and fun way to leave your mark on a space.
When you put it up - I furtively put it up at one in the morning the night before the first day of Spring semester classes. A friend helped boost me up and kept a lookout for passerby while I quickly stitched it in place.
What wool or other materials you used - I used standard red heart worsted weight 100% acrylic yarn (so it wouldn't shrink with the rain and would hold up well) with large needles so it would go pretty fast. I knit it flat like a scarf, then stitched it together on the pole itself.
Anything else of interest - The knitted sweater has gone through a couple of phases. At one point a couple months ago, someone cut the strings holding it up so it pooled around the bottom of the pole. (At the same time, another smaller piece I put up was taken down). Someone else pulled it back up and attached it at the top, but the stitching bunched so it didn't sit straight. It later fell once more. It sat there for a couple weeks and eventually the stitching holding it came undone and it sprawled open onto the sidewalk. A week or two ago a friend and I went down in the afternoon with a chair from our room and I stitched it up again properly (this time I took the time to be more careful so it will hopefully last even longer!).
If you want to see other sweater Guerrillas go to: http://www.spiegel.de/international/zeitgeist/0,1518,763843,00.html