Is that things change all the time, and keeping track of what's changed can be tricky. There's a list of Things You Shouldn't Be Doing In Rails over at the Gluttonous blog, and from that in the comments I found another link on using params and not @params.
This is all good stuff, but if people coming to the framework are relying on published books and tutorials, it's giong to be real difficult for them to keep up to date, if these corrections only exist in various blogs...
The best answer from the P.O.V. of the newbies is that the people who wrote the tutorials, go back and clean them up with the new conventions. That said, unless those guys are really altruistic, I can't see it happening.... it's one thing to write some cool tutorials for a new framework, it's quite another to have to go back and maintain them ...
Hmm perhaps the best answer is a listing of the conventions that've changed somewhere reasonably official and make sure it's clearly linked, I know I would've found it more readily than I found these items...
