I have a Dell Streak 7 which originally shipped with Froyo, but now has official support for Honeycomb. If Gingerbread to ICS is similar, the device's menu button still works, but you will also have another menu button inside native ICS apps.

I think the lack of a menu button on the Galaxy Nexus is a little odd. There's plenty of real estate along the bottom of the screen. It could easily be present and actually is when you're running an non-ICS app.