Well it's finally here. Drupal 8 will be released on 19 November 2015. I remember at my previous role at the Western Australian Museum we ran Drupal 6 for our main website, and Drupal 7 for subsites and ticketing applications. I made the call to wait for Drupal 8 to arrive before upgrading the main site, as it had "just around the corner" for, well, about two years. But it's finally coming.
A very exciting time. We'll finally be embracing OOP framework, Symfony, as well using Twig templating to remove direct PHP on pages. That said, my number one concern (and this is a big one), is that the Webforms module has not yet ported over to Drupal 8. For me Webforms was one of my favourite features as you could make sophisticated, scalable and powerful web forms with virtually no effort and integrate all the results into whatever other backend systems you've got running with not too much effort. Entity Forms (which is ready for D8) does not fit the same gap and does not offer the benefits to web publishers.
I suspect that until some of the key modules, like Webform, are ported, we probably won't get a massive amount of migration over to D8 for established sites. But that said, if you starting out, or don't need some of unported modules, now is the time to get a release candidate and start embracing the future of Drupal.
Personally, between my studies and fulltime work, I will probably wait until we have a critical mass and the key modules ported before upgrading. Also, I need to learn Twig and Symfony, which probably has to take a backseat due to my backlog of trying to other learn new things. Quite the backlog too.
But in the meantime, I am still very excited about the release and look forward to seeing what some of my colleagues and other developers can present at the next Drupal Meetups.