When people talk about the IoT, all I hear is "a massive attack surface that lets hackers do real-world damage". And really it is inevitable that the IoT will be insecure, at least the most elite hackers. There is no such thing as a secure system, and the wonderful thing about the IoT is that unlike a big safe where someone has to break into your house and actually move all your valuables, a hacker from halfway around the world can break into your delf-driving car and kidnap you. And the worst part is, it will be unavoidable in the future, unless you're willing to be called a luddite. There will be absolutely no real defense against a determined adversary. That is why the IoT scares me. Privacy issues are a big second.
I met a guy recently who works for Cisco, and he's pretty high up in the division pushing for IoT. I mentioned that I thought that it was a nice buzzword but that I didn't think it was going anywhere. He of course disagreed. I then questioned whether it was possible to avoid being a complete security nightmare and he threw out a bunch more buzzwords trying to convince me that Cisco had figured that out. I was not convinced.