I think it's great that Firefox is bundled with Ubuntu, but I have to manually update Firefox each time a new release comes out because the version that's installed is a canonical-controlled version that stays 'stuck' on a old version and doesn't have an auto-update mechanism.
Other than that, I love the OS. I use it as my daily driver since it has a good community around it, and if you're having trouble, there is a good community-powered Q&A site for it.