You are a bit unprecise. You tell us that haven't seen one useable decentralized application? There are a few...The primary example that I came across is Gridcoin and BOINC. That is a working application. But just in case you mean that u don't know an example of an ethereum based application.Then I can agree that I'm missing those as well atm. Conlcuding just from this, that ethereum is a scam...Is not enough for me. In my opinion the main problem is that the most of the "companies/ICOs using ethereum are still in very early stages. Software development is not that easy. And atm, there are not that many software developer that are capable of programming in solidity. So... at the end.. imao it is to early to judge.