Serversite error handling, rails "compatible" validatotors, new event callbacks, validator generation from rails and more

Dmytrii,
My colleague Krzysztof Madejski has upgraded your nice tool for use in our project. I have rewritten specs to mirror the changes. I would like to ask you to have a look. Merge or give me some guidelines as what to change.
Thanks in advance and thanks for knockout-rails. 
Jan