Adam Milligan's blog
Nested attribute assignment is one of the recent additions to Rails that made a great deal of sense, and made a lot of people happy. Chances are you've either used nested attribute assignment by now, or you worked on an older project that really could have used it. If you haven't yet, check it out and see what you think.
Unfortunately, not all is well in Railstown. Nested attribute assignment is slick, and the related implementation of #fields_for makes it even slicker, but #fields_for can cause you some headaches if you're not careful. Possibly if you are careful as well.