A few off the top of my head: laptop touchpads lacking full functionality, keyboards with Fn key functions not working, poor power management support. Some laptops still ship with WLAN hardware that doesn't work out of the box.
None of this stuff represents a complete dealbreaker, but it's a combination of factors that wears down the likelihood that I could adopt Linux on a personal PC. As a VM? Something I remotely manage? No problem. But when power management is so bad I only get half the battery life I get on Windows AND the screen brightness keys don't work AND I have to go make my own gesture to get the touchpad to middle click or something, it's pretty hard to say it's worth it.