The OS X shortcut for quitting an application is Cmd+Q. The shortcut for closing a window/tab is Cmd+W. Q and W are adjacent on a standard QWERTY keyboard, which means you sometimes hit Cmd+Q when you meant to hit Cmd+W.
Now hitting Cmd+Q accidentally doesn't matter most of the time. Most applications will ask you if you want to save your changes before you quit. Web browsers will offer to save your session. Also, most applications save their state anyway, so you can relaunch them and continue working. So not a problem, right?
There is one piece of software, though, that refuses to follow this convention. A program that has ignored every HIG and UI convention in the history of all known universes in the name of creating a "better" user experience: Google Chrome.
I didn't complain when they hacked the window system to put tabs on the top of the window. I didn't complain when their shitty multi-process model brought my aging MacBook to its arthritic knees. I didn't complain when they opened PDFs in the browser without asking me first, or when they used filetype associations from my OS instead of letting me redefine them. But this just takes the cake: Google Chrome will quit without a confirmation if you accidentally hit Cmd+Q when you meant Cmd+W. In the last month I've accidentally quit the browser twice, and lost about 50 tabs every time. Surprisingly enough, there is no extension that will fix this behavior. Yes, a couple of hacks exist, but they only work half the time.
I don't expect Google to fix this, though. There are gaping holes in Android that Google has simply ignored or outright refused to fix. I don't expect them to treat Chrome differently.