This site '[Buddhist Texts](http://www.uwyo.edu/religionet/er/buddhism/btexts.htm)' 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:

1. Is Tipitaka taught and learnt by monks in monastery?
2. 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)
3. Are laypeople encouraged to learn Tipitaka?

These are just guidelines. One might use their own criteria. Answers from different Mahayana schools are welcome.