I'll keep this post short. If your website is running Drupal 6 I would recommend an upgrade to Drupal 7 or 8 as soon as possible, since it has already reached its end-of-live. That means no more security fixes or community support for Drupal 6 (see Drupal 6 end-of-life announcement).
If your website is running Drupal 7, then there is basicly no need to hurry. Drupal 7 will be supported for years to come and not all of the major modules have been completely ported to Drupal 8 yet (see list below).
- Panels (beta4)
- Panelizer (alpha2)
- Rules (alpha1)
- Media entity: (beta2)
- Entity browser: (alpha2)
- Inline entity form: (alpha5)
[list updated Mar 21 2016]