I\'ve been dealing with a spate of Timeout\'s from TopicClient and I think it may be related to object lifetime and disposal.
I\'m using the TopicClient
Just to add another confirmation from MS that this is thread safe, from Best Practices for performance improvements using Service Bus Messaging:
You can safely use the QueueClient object for sending messages from concurrent asynchronous operations and multiple threads.
They don't mention TopicClient explicitly, but would expect the same goes for TopicClient as for QueueClient