The writing has been on the wall for delicious for years. They never made any money, never found mainstream adoption, never made use of the enormous flow of user sharing data they were getting to do anything interesting. They have been operating on a skeleton crew for years. Such a shame.
My mom knows what delicious is. That's pretty mainstream in my book.
We don't know your mom, so that doesn't really contribute anything to the discussion. What's she like? What's the most mainstream web site she doesn't know about?