When to stop funding a 529

Any thoughts or guidelines as to when the amount of funds in a 529 may be considered sufficient? Of course it will depend if the child goes to public or private (or no) college, grad school, etc., and I am also aware of the new rule that some excess funds (up to I think $35k) can be rolled into an IRA if certain criteria are satisfied. Given all that, when do folks consider a 529 adequately or fully funded by age of the child?