It used to be called an "unveiling", and the gravestone would be covered over with a pillowcase or something, but that's just an American custom, and they're trying to phase that part out. Having a ceremony about a year later and formally "setting the gravestone" (actually done professionally and in advance) - that's still a mitzvah.
It was just the five of us - Jonathan, his parents, his brother, me. Jonathan did the service, saying the appropriate prayers and a couple of poems and a brief sermon and then we put stones on all the stones in the family plot that had meaning for us. We also spoke to the family in the plot across the way and I looked at various gravestones. Most were what you'd expect "wife, mother, grandmother, great-grandmother". Others, though - "son and uncle." "Son, grandson, nephew." "Wife and sister." The ones who never married or never had children. The ones who died at the age of 31, with the inscription "At rest at last", and you want to know the story. Or the thirty-five year old with a small boy's nickname. You want to know that story, too, and you can probably guess.
My husband's family has ivy planted over the graves. The longest planting belongs to Jonny, who died before the age of four. So there's sadness there, too.
I find gravestone settings to be important - they give a sense of closure. Mom began the setting crying about how her brother shouldn't be there yet, but by the end, she was relaxed and even laughing. Dick is gone and we miss him terribly, and the world is a poorer place without this brilliant polymath, but life goes on, and the time for mourning is past.
Afterwards,we took my inlaws to one of our favorite restaurants, a brick-oven pizza place. It proved to be just the right place. M the veggie found a wonderful ravioli dish, Mom, who is low carb for health reasons, had a salad with carmelized onions and blackened tuna and Dad will eat anything. Afterwards, I went with my inlaws to the local kosher supermarket and helped out as they bought enough meat for part of the summer.
It proved to be a lovely day.