A simple way to get the event loop working is

library(gtk)
.C("R_gtk_setEventHandler")

Then 
gtk()
plot(1:10)

and resizes, expose events, etc. will be handled.

If using the RGtk package, one can use the asGTKDevice() function
easily. The devices.S file in the examples/ directory can be used
to show a notebook containing multiple pages of different configurations
of devices. These include
  a) a scrolled device
  b) a dynamic paned layout containing devices and grips with which one
     can adjust the size allocated for a device. This is like an interactive,
     re-sizeable version of layout().
  c) a regular device in its own page.