In the US, it's often possible to find the gravestones of ancestors going back for hundreds of years, scattered across the country in various cemeteries. This makes genealogical research a little more fun, in that you can track down some physical remnant and memorial of the people you're looking for, and of course it also helps verify names and dates.
It never occurred to me that the same thing wouldn't be possible in other countries.
Here in Sweden we have really good records that are open and free to search online. The church kept an eye on everybody back in the days so the only obstacle is not being able to read some priests old handwriting from the 1700s, or that everybody had the same names back then, "Anders Andersson" might be the worst example of that. I hope AI will take care of that, probably any day now. Might take some of the fun out of it though.
My mothers grandfather that died in 1938 still has his spot, it is going to be there for a few more years. I don't think anybody has visited it for a very, very long time. My mom didn't even know it existed until I found it online, so at least 60 years. I think the standard "lease" was for a really long time back then, and now when the grave yards are overcrowded you have to renew it every 10 - 15 years by default. A lot of people probably makes the first grave into a family grave. So you'll have grandmother, grandfather, father, mother, fathers second wife (awkward :P), and so on in the same grave.
The furnace that heats his home is more likely fueled by natural gas, however the combustion chamber where that gas is being burned may also be used for cremations.
I'm pretty sure that humans make pretty lousy fuel.
twain
Aside from moral/cultural qualms and a difficulty achieving scales of efficiency, there's no reason human remains couldn't be used to produce perfectly usable biodiesel.
We're good mental fuel and I wonder sometimes if there is any liveform in the universe that feeds on that (god ;p).
My father passed last week, maybe he heated up a small part of Stockholm already. I don't really know what happens next. Personally I don't care that much, I got my memories and that is enough for me. But based on what happened to the rest of my dead relatives he'll get a small plate with his name on at the corner of some church yard. It will be up for x years until they have to make room for the next batch. You can always pay to keep it up for maybe five or ten more years, but what is the point? Memories are free and worth way more than the tiny nameplate.