I put a piece of plywood on top of my dining room table (which already has a table cloth on it) and use many, many binder clips to secure the quilt to the plywood. That way I don't damage the table and if I don't get my quilt completely pinned before mealtime, I can just move it without fear that the quilt will shift.
If I'm making a really large quilt, I divide it into quarters and pin a quarter at a time starting at the center of the quilt and work my way out.