Interesting Things
application.rb vs. application_controller.rb: As we all know,
ApplicationControllerbreaks with Rails convention and lives in theapplication.rbfile, notapplication_controller.rb.Be careful if you create anapplication_controller.rbfile of your own, as this can confuse Rails class loading and might result in Rails deciding not to loadapplication.rb.Google Webmaster Tools: Note that if you are using Google Webmaster Tools that statistics are different for www.example.com and example.com (sans www).

Nested Model Forms are coming in Rails 2.3! There is even a patch in progress.

You can specify which domain to use in Google Webmaster Tools settings: http://img.skitch.com/20090127-gj3194f14dp1sfcynqm6ar9it5.png
Love the screenshot :)
@Dmytro
The issue wasn't with how the urls are displayed, but how webmaster tools shows us the crawl stats. For one of our clients, one domain shows a average crawl of ~1,000 pages a day, for the other domain it shows ~90,000.
Even though the non-www version had the sitemap added, and google was crawling those urls, those crawls weren't reported because they were only being reported for the www version (which we didn't have added at the time).
I think that it is always worth adding a permanent redirect from the less favored to the more favored fully qualified domain name of your sites.
If your client wants to be example.com, then redirect traffic from www.example.com to example.com. This is good for both the client's branding and their page rank. Plus you don't end up wondering who is crawling your pages, what your total page views are, where your ad sales were, etc.
It looks like nested models support has been officially added to Rails 2.3! Read about it in Ryan's Scraps, the github commit, and also the official blog.
@Ray
We've had a permanent redirect in place since last March, but the crawl stats for example.com still have ~1,000 page crawls a day.
This is why at first we though the stats MUST be unified, since how could Google be crawling 1,000 pages a day, all which return a 301 response.