ogr2ogr for converting postGIS layer to shapefile

Hi Murray.
About the first question. As far as I understand, you're working in R
on a *imported* PostGIS layer (I suppose you use rgdal to do it,
right?). Then you would need to export it to a shapefile (easily done
with writeOGR). Why are you considering the use of ogr2ogr? As you
probably  know, it's a binary callable from a command line, and it's
not possible (AFAIK) to do it from R...

I dont' understand your second question...

Or even better could ogr be used to do this directly on a postGIS layer?

What do you mean?

Giovanni