Re-Nesting: To have or have not a contract with your adult children

Parents of 20-somethings--especially recent college graduates--are experiencing a steady march of children returning to the nest. It's a hostile economy out there: difficult job market; horrendous credit crunch; rising prices for everything. And it's not just the 20-somethings, as the reports noted in earlier blog entries make clear. But all that raises the question of what sort of rules should parents set when the kids come back to the nest.
An interesting discussion of the issue is in a recent College Times story:

Written contract or no?  "Experts say there is no right answer because the dynamics of each family are different." That said, CT's experts say, it's important "to have a plan, preferably in writing, that spells out the new relationship. It can be as simple as a contribution toward household expenses, or it can be chapter and verse, but the reunited family needs rules."
One of the experts quoted is John  L. Graham, a business professor at University of California at Irvine who co-authored a book about the move-back phenomenon, "Together Again, A Creative Guide to Successful Multigenerational Living." It's not only about young adults returning to the nest but elderly parents moving in as well.