Although I had read in some forums, that all that green button written with Econ on it in Honda car's is turn on a green sign on the instrument cluster. It does not improve anything much. Few weeks ago, a fellow pakwheeler mentioned very good economy without econ button 'ON', so I decide to try it my self. Well I have alternated between the two modes twice each, between fill up over the last 1000km+. And to my surprise there is absolutely no difference in fuel consumption between these both!!
These are under very similar driving conditions within Islamabad, with similar loads on the vehicle. Consumption was calculated by distance covered and fuel fillup (Super) and remains 20kmpl for my GP1. One thing I will mention here is that in current weather neither the AC or heater is being used, so I can't say whether having either of them on will give a different result.
The improvement in acceleration without econ button on is clearly noticeable. Although one gets used to it, and eitherway, that ever was or is any issue.