I think there might be a somewhat involved solution to the problem of integrating mac osx menus in inkscape. Sure having Inkscape with mac-ish menus would be nice.
It entails creating an invisible window with a menu that is managed by OSX-integration. When a menu event is generated, the invisible window delegates the event to the windows that has focus - either via programmatically triggering the window's own - invisible- menu or by directly calling the verb/action.
Valerio
Your email, unfortunately, made me think that OSX menu integration might not be possible, without a major rewriting of the source code. Inkscape's architecture (as for the majority of gtk apps) assumes that, in multi-document mode, every window has its own private menu that receives and process events.
In OSX, in multi-dicument mode, there is only one menu that processes events and dispatches actions to the window that currently has the focus.
It might not be possible to achieve this type of integration with the current state of Inkscape' sources.