I guess if your rooms have no direct/indirect light they would be a big boost. (we have glass block in both showers that seem to act like a solar tube!)
But they would take a long time to pay for themselves in energy savings if someone is thinking about that aspect. i.e. if you saved and extra 400w of energy for two extra hours per day your savings would be about $30-40 per year (depends heavily on kw/hr price but that was my latest research using my bill). And I think most people wouldn't even use an extra 400w, probably closer to 150 and that would only save about $15-20 per year.
But they do last forever I guess.
For reference:
http://michaelbluejay.com/electricity/cost.html