I certainly have done it. Needs good weather though, as well as a good middle of nowhere. I also went through a phase of taking a flask of tea with me. Haven't done that for a few years either. I found the first cup or two were good, but then at a subsequent stop, it would all have gone cold. Also, it depends on the 'type' of ride. Not just racing, but (for me: Graeme I suspect is fast enough to have time) there's no time for this on an audax. Electric kettles are faster than camping stoves! Besides, I wouldn't have a stove with me – unless I was camping, in which case, well it's obviously part of camping.