I recently upgraded this site from Drupal 7 to 8. It was relatively painless, although I didn't actually do an upgrade. It was a fresh install with some selective copy and pastes of a few posts I have written. I also added Disqus and abandoned Drupal's core commenting system to try and deal with spam.
So far, so good. One thing I noticed is that there are very little modules or themes available for D8 which I guess is to be expected considering there isn't a release candidate yet.