I've mostly gotten over all the confusion in Windows and Linux, but OS X still confuses me. Specifically how to install an application. It seems like it's different with each app.
For example, I downloaded a .dmg file for the Transmission BitTorrent client. And I double clicked it. There was another icon inside, and I double clicked that.
Now I'm running the Transmission client and I can use it. But it's not installed? I can't click on a .torrent file and have it launch the client.
I try to drag the whole thing into Applications? That makes a big mess. It doesn't install it. I have to open up finder and manually remove the files.
Then I realize I have to click the .dmg and then drag the thing inside into Applications.
To me everything in OS X looks like an "icon" and there is some tenous relationship to directories/folders, and "Applications" is some special pseudo-folder. I'm still confused, and not surprised at all that end users are confused. And this is on the OS that's supposedly the most user-friendly.