I see the same warnings you lot see: Eventually this will destroy your engine and void your warranty, etc etc. If that was really true, then how do these 'experts' account for the thousands of owners for whom none of this happens? The computers and ECU in your engine will run that engine as well as possible based on the octane you give it to work on. But you won't benefit in any way other than saving about $5-7 per fill up. Thinking along those lines, consider this. That's one cuppa coffee at Starbucks,one fast food lunch, or even one pack of cigarettes. Also, although the engine 'should' account for and perform on regular octane, it cannot run as efficiently, which results in lower power output and decreased mpg ... so your savings at the pump are not as big as you may think. For me, I would give up one stop at Starbucks or one meal at Wendy's and let the car be.
And, as always, if you're on holiday and it's a rental ... I follow Jeremy Clarkson's advise: drive it hard, return if filthy, and use the cheapest crap petrol you can find, LOL.