Importance of Tipitaka in Mahayana Schools This site 'Buddhist Texts' says that while Mahayana schools revere Tipitaka as holy texts, they add many other sutras, the most famous being the 'Lotus Sutra' and the 'Heart Sutra'. My question is how important are Tipitaka in Mahayana schools. One may gauge its importance based on:


Is Tipitaka taught and learnt by monks in monastery?
How often Tipitaka is referenced in lectures by monks? (for e.g. I was once listening to discourses of Dalai Lama and he was talking of Nagarjuna, Milarepa, Ashvaghosha etc. It might be that he did not reference Tipitaka in those lectures but might have referenced in some other lectures)
Are laypeople encouraged to learn Tipitaka? 


These are just guidelines. One might use their own criteria. Answers from different Mahayana schools are welcome.
Tripitaka is taught to and learned by monks in the monasteries and laypeople are encouraged to learn. From a Tibetan viewpoint, the texts H.H. quoted are included within one of the three baskets. Shantideva's Bodhisattvacharyavatara is included in the Sutra Pitaka (although it is not a sutra), Asanga's Mahāyāna Sūtrālamkāra kārikā is included in the Abhidharma Pitaka, Kamalashila's Stages of Meditation belongs to the Abhidharma Pitaka, Nagarjuna's Karika belongs to the Abhidharma Pitaka as well, and so forth.

In the ninth chapter of the Bodhisattva Deeds, Shantideva explains that anything that is included within one of the three baskets was the speech – or at least the intention – of Lord Buddha. His Holiness the Dalaï-Lama highlighted this principle. In Illuminating the Path to Enlightenment, he writes:


  As Dromtönpa lay dying, his head rested on the lap of one of his chief
  disciples, Potowa, and he noticed that Potowa was crying. Then Potowa
  said, “After you pass away, in whom can we entrust our spiritual
  well-being? Who can we take as our teacher?” Dromtönpa replied, “Don’t
  worry. You’ll still have a teacher after I’m gone—the tripitaka, the
  threefold collection of the teachings of the Buddha. Entrust yourself
  to the tripitaka; take the tripitaka as your teacher.”



Furthermore, in 'Transcendent Wisdom', His Holiness writes:


  The three baskets are (1) Vinaya, dealing with moral discipline; (2)
  Sutra, dealing with the training in meditative concentration and other
  facets of the path of awakening; and (3) Abhidharma (sometimes
  translated as "higher knowledge"), concerning a diversity of topics
  ranging from psychology to cosmology. For a further explanation see
  Opening the Eye of New Awareness, pp. 47-52.



We hold that the Tibetan translators showed to which basket the text they were translating belonged, by way of paying particular homage. As His Holiness writes in his commentary to Stages of Meditation:


  The intention [of the Tibetan translator paying homage when
  translating Nagarjuna and so forth] was to cearly indicate to which of
  the three divisions [the pitakas, or baskets] of the Buddha's
  teachings any sutra or commentary belongs. [It goes as follows:]
  1. Supplication is made to all Buddhas and Bodhisattvas if a text belongs to the Collection of Discourses [i.e. Sutra Pitaka].
  2. And if a text belongs to the Collection of Knowledge [i.e. Abhidharma Pitaka], supplication is made to Manjushri.
  3. In order to indicate that a certain text belongs to the Collection of Discipline [I..e Vinaya Pitaka], supplication is made to the
  Omniscient.