I don’t have any vested interest in NServiceBus. Sure, I wish it were free. I would be more than happy to start using it in many projects. Open source is not about being free, and Eric J. is 100% wrong in his statement. Open source is about transparency, namely opening up the source code. The NServiceBus project does that.
The #1 input to quality software is exposure. As humans, we are fallible creatures. Even the best of us will make mistakes. Even really big, highly-funded projects have problems. Do you think that Oracle or Microsoft have never released a bug?