I first heard about yarn bombing last year, when Bellevue, Washington, got hit.
Then, last week, I had lunch in downtown Seattle with my friend Julie. We went to a place we'd been to before, a little soup and sandwich shop near Occidental Park. The yarn bomber had been busy there as well.
My understanding is that the installation stays there until it disintegrates. In the meantime, however, Julie told me that the homeless people who congregate in the park are very protective of it. She said that it's not often that people come along and beautify their environment.