I don’t like much Adobe, but their commitment to Linux is above average. Flash for Linux never was great, but at least was close to their pairs on Windows.
The problem was with Flash videos, which is now the vast majority of its usage. The problem relies on pure CPU processing. The Linux version does not use the video card to decode the highly compressed videos used today. The result was a slow computer when seeing videos. The situation was really dire when you attempt to see more than one. The crash is almost certain.
But finally my days of browsing YouTube or porn sites only on Windows (which is a quite risky) are over! The new beta version of Flash (10.3) finally uses the GPU and is several times more stable. On KUbuntu, I added the repository ppa:sevenmachines/flash and installed the flashplugin64-nonfree package.