[racket] Declarative Prototype Object Extension - looking for feedback

I'd always found prototype object systems interesting, and thought
they might be a good fit for racket - so I made one about a month or
so ago

Features:
- Prototype based, no distinction between classes and instances.
- Multiple inheritance, methods are looked up in depth first search
- Declarative syntax, can create an object with a single macro, no need to clone
and mutate
- Immutable objects, which can be inherited by and inherit from mutable ones

https://gist.github.com/4605785  - go to line 195 shows its usage.

Basically, I am after feedback on my code, the concept in general, and
anything really. I actually use it over the  java-style class object
system racket has, it's very much my vision of what objects should be
like. But yes, any feedback would be welcome.