I know that as per the story (like found in Shiva Purana: Rudra-saṃhitā: Yuddha-khaṇḍa: Chapter 40) of Shankhchud killed by Shiva, it was banned from his worship.
But still I have seen many people, specially in Varanasi's sandhya aarti and in many temples of Lord Shiva from south India, brahmins are using the conch shell frequently.