Personally I haven’t. While Linux is imperfect, choosing the right distro makes the rest of the experience straightforward. And with it’s whole complexity, I find Linux more user friendly than Windows. Even driver issues, broken shadow file ownership and KDE specifics only made me more confident about my choice to use Linux after I solved everything.
In the old days, lots, mostly around hardware support and until very recently the ability to run most games.
Nowadays, I’m mostly disappointed with the desktop environments lacking features that BeOS had in 1997. This is honestly a kernel and filesystem issue since most of those features require that the kernel/filesystem fully support indexed, extensible attribute queries. xattrs aren’t nearly sufficient. The remainder are framework/UI threading model limitations, which aren’t really kernel related.