I'm too busy listening to the '50s, '60s, '70s, Escape, Sinatra or Classic Jazz on the XM radio to care what mode I'm in. At most, the difference in mileage would only be 1 or 2 mpg. Once in a great while I'll select the Power Mode so I can glance at the tach and try to imagine that I'm actually in a car that needs a rev counter, but for the most part, I leave the selector alone.
If I was a lot younger I might choose the EV mode a quarter-mile from my digs so I could slither into the driveway after a late night poker game without waking the wife, but those days are long gone. If they weren't, I'd probably be on a Fiat 500 forum instead of this one!