That's the trouble with the evidence for this being a problem - it's extremely scarce. Even that linked from the title to this item just surveys the wattage - they didn't monitor actual usage. Nor did they allow for the saving in heating costs in winter. I doubt that there's much of a real saving there. Also it's a real fuss to have to pay attention to - on a par with saving bits of string - and needs a wartime mentality.
More sense perhaps in looking at enegy saving lightbulbs? A 100w lamp used for 4 hours a day consumes 146kw in a year, costing £12. If I can save 75% of that for a cost of £3.50 ... and then the bulbs last another 8 years ... even if the heat is useful for 6 months of a year, it's a clear winner.