Been running Ubuntu for quite some time now. No problems, no issues. Occasionally, some Windoze dominated site won't load properly, but that's obviously their problem. In the past, I have had issues with the 64-bit distro (I use 32-bit). The normal user won't see a difference here anyway.
Make sure you've got the flashplugin-nonfree and ubuntu-restricted-extras packages installed. I've been running Linux for a long time now. Started with Slackware, went with Debian for a while, tried several others. Ubuntu is a good stable distro.