The migration for me was straight-forward. Look at what's new in the framework and move items across. The biggest challenge that i've found was the MVC code.
We deliberately de-emphasized getting migration completed for this preview release, but will have a ton of documentation and help around this in an upcoming release
jgarcia@tdg-i.com i'm going to work on migrating my app today and see how i get on. We've got a cut down CSS and optimised jsbuilder sencha build so probably best to leave all this behind and just look at getting the code up to scratch on the full versions of 2.