We launched a new site on Monday, September 9, and as of last night, it was listed on Google already! There is a link on the front page to another of my websites which gets crawled once a month and has a PR of 4. That's the only explanation I can think of.
I have had the same experience. I launched a site the other day, hoping it would get into the next crawl, and within days it was appearing in the top results for my keywords. It doesn't even have a page rank yet. But I have been linking to it from sites with a PR of 6 so this might help. I was always under the assumption that the dance was the time when completely new sites were added?