Well, it doesn't exist. Yet. And never under that name - it's now known as the "gentle introduction". But it's essentially the same thing: comprehensive coverage of the most commonly used bits of Symfony - not too vigorous, not too limited and not too example based. An excellent middle-of-the-road reference.
The only problem is it's not quite finished. But, luckily, it's now at github. This is great for two reasons. Firstly, it's not too bad viewing the latest version right on the site - it's written in markdown, which github understands and displays nicely. And secondly, it makes is super easy to fork and correct any problems that you come across while you're looking stuff up.
Edit: The guide has now been finished and is available here.