Hi Siddhartha,
HANA is widely used in many scenarios. Most commonly it is used as the underlying database for BW application with additional use cases for the Native HANA side. It is also being used for the underlying database to ECC.
Some of the transactional applications are also ported to SAP HANA.
Your question is quite wide and open. I am sure you can find specific use cases on www.saphana.com.
Ravi