Ruby on Rails app on Google App Engine

Can anyone give me some pointers on how I could deploy my rails app to GAE? I've been reading about it, but it seems to be a fairly complicated task.

I tried with the google-appengine gem, but its not a piece of cake either.

Has there been any progress with the DataMapper adapter or will I need to make changes to my models?

I was hoping to see a full-detail tutorial about it, but those that I found were somewhat out-of-date.

Deploying Rails on Google's App Engine has become a lot easier than it used to be. There are a couple of caveats you should be aware of:

• App Engine only supports the Python and Java environments so for Rails you will be deploying on JRuby
• App Engine's datastore is based on BigTable so you won't be able to use ActiveRecord on a relational database (if you want your datastore hosted in AppEngine). But as @Geoff Lanotte as pointed out there is a Datamapper adapter you can use
• Pre-deployment testing is done within Google's sandbox tools as opposed to things like script/server

Some other resources you might consider:

http://code.google.com/p/appengine-jruby/

http://rails-primer.appspot.com/

http://gist.github.com/335023