Better version of the BlenderGuru tutorial you can find here:
Do a search for 'Bounce Lighting' and you will mostly get information on how
to use reflectors to bounce 'fill' light into a photographic setting, largely to add
light into shadow areas. But from a CG perspective, 'Bounce Lighting' is about
how to fake reflections from reflective surfaces (the barrels here, but quite often
simply the ground surface) into shadow areas (or otherwise, but anywhere fully
lit will not show Bounce Lighting or at least that's what my real-life experiments
seemed to show). For a real challenge, try shag carpeting as it will have areas
of both heavy shadow and fully-lit strands of material.
Some very good examples of the affect of reflectors here:
[Kevin is not using the reflectors for 'Fill' but 'Key' lighting, I found this series
very helpful in terms of understanding the affect of a given reflector colour.
So using these reflectors in this way makes this easier to see, but I believe
reflectors are more normally used to add 'Fill' light or just to smooth out
any difficult lighting scenarios.]
Comments on my success (or failure) with bounce lighting are very welcome.