I've been getting the "EV mode not available" message from my 2010 RX450h, which I bought a couple of weeks back, only slightly used (under 15K miles). My latest attempt at using EV mode was this morning, as I was pulling into a parking lot at low speed. Our '12 Camry hybrid has an EV mode button; you don't have to navigate a menu to turn it on. But I find it superfluous in any case. The Camry will go into EV mode by itself -- signified by an "EV" light on the instrument panel -- whenever it's warranted. I agree that driving style is the best way to maximize the car's use of electric power instead of gas. I've been keeping the instrument-panel multifunction display set on the screen that shows the wheels, ICE and battery. I try to keep the power arrows coming from or going toward the battery as much as possible by feathering the accelerator and coasting the car, without hyper-miling and becoming a nuisance to other drivers. (This mainly means that I observe the posted speed limits, which many other drivers unfortunately find to be a nuisance.) I'm averaging 28 mpg the last I checked.

Our Camry hybrid displays average mileage per trip on the instrument panel whenever we put the car in park and turn it off upon arriving at a destination. The car even congratulates you when you do exceptionally well, like when we do better than 41 or 42 mpg in town. I wish the Lexus had an instrument-panel display like that. It's a great way to keep score.