You should all go read Ms. Lee To Be's thoughtful blog post about tradition, in light of the picture of a pizza on a jesa table, that made the rounds on Korea's internet recently:
the main gist: we preserve dead things. To make preservation (rather than practice) a goal is also, in part, to surrender the belief that tradition remains relevant to our lives.
The Korean from Ask a Korean! wrote about how to do a Jesa a while ago, and has a (short) response to the pizza jesa here.
I wrote about Jesa once, a long time ago, too, upon reflecting on my mother's death of cancer.