Mine has averaged 4.1l/100 over 35,000km. Petrol today is $1.70/litre (regular - Premium is $1.93) - and yes, I'm pleased that I can get almost 1000km on a tank - unlike the chaps who bought Twin-Cabs or SUVs - to drive alone in many cases. The only difference I've noticed with l/100km if you went to POWER rather than ECO is in using DRCC - it'll more aggressively keep the speed up hills, where ECO may lose speed a little - but the difference is likely to be small, if measurable at all.
Old thread, but I'll chime in. I like ECO mode, because it's easier to modulate to keep it in the electric range for local driving. This often gives a huge advantage in economy. In local driving, I'm quite often able to keep above 70 mpg. On the highway, I never get less than 50 mpg, and usually 55. Anything nearing 40 mpg and you might as well be driving a conventional car at that point. On the highway, the engine is on most of the time anyway and I admit that ECO mode just makes it more work. Gotta FLOOR IT to get decent acceleration. POWER mode makes it more touchy and less smooth; I don't like it. Maybe I'll try it on a nice twisty road some time.