Today the Drupal project reached the grand old age of fourteen. This is a great milestone for the community and the project, and in celebration, the Drupal association has released the results of their 2014 Community Survey. Among the insights:
80% of Drupal Users who responded say they have plans to adopt Drupal 8, and another 8% say they are planning to evaluate the new release.
Upgrading is an inevitability, because "the drop never stops" - i.e. there's no backward-compatibility in the Drupal universe. But personally, I've always waited about a year before recommending major upgrades for my Drupal-based clients.
While the core system is typically solid and the upgrade routine fairly straightforward, the same cannot be said of all the contributed modules, especially with the dramatic changes we've seen in recent upgrades. New database schemas and UI subsystems take time to learn, and that time should be spent learning - not programming badly for other people. I've been working with Drupal since version 4. In my experience, it will take about a year for the community of contrib developers to get their new versions all playing nicely with each other, and with the new codebase.
Drupal 7 will continue to be stable and supported for many years. There's no rush. Let the first wavers be the guineapigs, I say.