From the top of my head the following examples come to mind.
1. Early criticism of the tablet was that nobody would use them because they didn't have a keyboard.
2. Early criticism of the internet was that nobody would ever purchase anything over the internet.
3. Early criticism of dropbox mentioned elsewhere in this thread, "they're just re-selling S3, why would anyone use that".
Disclaimer that I'm pretty deep in the Ethereum space so my perspective is anything but objective, but it is informed as I know the space quite well.
Smart contracts are capable of big transformative change to how we do a lot of things, but they are REALLY new and we're only just starting to learn how to use them and what we can use them for. Here are some examples.
1. Look at [ENS](http://ens.domains/) as an example of what DNS might look like if it weren't centralized.
2. Look at [simple Escrow examples](https://dappsforbeginners.wordpress.com/tutorials/two-party-...) for how smart contracts can remove middlemen from financial transactions.
None of these things are likely to blow up into massive mainstream adoption tomorrow but they are illustrative of what is possible and there are a lot of people working very hard to make these things ready for mainstream adoption.
These sorts of things are trivially gamed and have been since they were first proposed in the bitcoin space. Besides that you don't even remove a middleman for this example since you still need the courier to act as the middleman.
In my opinion what's really missing is a fiat currency token, that can be legally recognised as actual money for a lot of business to be able to go massive.
Do you have any examples of projects that would be truly different or impossible to implement without smart contracts?
It is unclear how blockchain smart contracts contribute any value to the users in this case.