Funny, I was thinking something similiar when in the "Twilight State of Mind." However, I am also thinking without mechanization alot of the cemetaries could and would be farmed by HAND since fuel to run modern mechanized farm equipment would be rare at best.
And there has been a big push in cemetaries here in the US to eliminate the monuments and head stones, now modern ones have flat stones that are flat in the ground at ground level. This is made for ease of maintenance and to reduce the indicence of vanadalism. An example, the Holly Cross Cemetary in Down Town L.A. is one such and it has been for about 50 or 60 years. And the same goes for "national cemetaries." Only the older ones pre WWII have upright headstones, most others now have headstones that are slat and level with the ground.
As for modern burrials in the post T2K world, it all depends. A community where the dead are known, they may continue to use the community cemetary, or even set one up in the community. This could be done in an area where a section of land is not suited for farming. I could also see a return to crypts or vaults, using basements, sewers and underground garages or caves and abandoned mines. I can also see people in or on waterways using bodies of water to burry them at sea.
If the people are utterly callous or mass graves especialy for people they do not know, they could make mass graves,
A mass body dump at sea. Toss them all on a barge in a sack with a large rock and over they do. All tossed in a pit or hole and burried <again see a large cellar, cave, tunnel or underground garage> or possibly even a burrial mount, burrying bodies in the plentiful ruble that was once the local city.
I personaly am thinking that for mass graves of strangers they would just without ceremony or any attempt at dignity just stuff them in a preexisting hole like cellar or such and then block it off.