[zrail]

As far as I know burial plots are not reused in the US. You generally buy the plot in perpetuity.

[maxerickson]

It varies. There are sometimes problems with private or small cemeteries that are run by an association running out of funds (or the association can end up with no members left).

A search for "cemetery disrepair" returns lots and lots of local news stories.

[cdcarter]

People buried stacked is not entirely uncommon in the US though.