Drupal is an open source framework for building amazing websites. Like most software companies, the Drupal community supports the most recent two Drupal releases. Currently the community supports Drupal 6 and Drupal 7. Drupal 8 is planned for release September 2013. Once Drupal 8 is released, the community will begin phasing out support for Drupal 6.
What does this mean for your Drupal 6 website?
If your website was built in Drupal 6, bug fixes, security and feature updates will no longer be maintained by the Drupal community. Sites running Drupal 6 will become increasingly insecure and vulnerable to malicious attacks and will also become obsolete in style and functionality. Unless the resources are available to maintain the Drupal 6 site privately, upgrading to Drupal 7 is a must.
Remember One year in real life = 7 years in technology.
So what will a Drupal 7 upgrade do for your site?
Drupal 7 includes security upgrades, wider theme support for HTML5, device agnostic design, easier access to administrative areas, improved WYSIWYG editor integration, more drag-and-drop for administrative tasks, permissions that include a description for easier management, and setting up automated task runs (cron) can now be achieved via Drupal's configuration for easier management. Drupal 7 also includes a redesigned password strength validator that makes it kinder, gentler and clearer. Drupal 7 includes better support for search engine optimization and web linking, added RDF and micro data support help that ensures compliance with the newest standards in search engine optimization.
So if you have not done so already, in order to keep your website modern, SEO compliant, device agnostic and secure, upgrading to Drupal 7 is a must. At this stage in the game any of the modules that are going to be upgraded from Drupal 6 to Drupal 7 have probably been ported. If they haven't, they may never be or you may need to volunteer time or money to port the module to Drupal 7. Some modules have been integrated into core, others have been replaced with other modules, and some have been discontinued for any number of reasons.
Why can't I just go straight from Drupal 6 to Drupal 8 when it is released?
I would not recommend this for a number of reasons. When Drupal 8 is released, it will not have full module support, so if you have anything beyond a core install of Drupal and some of the basic modules, you will not be able to duplicate the full site until the necessary modules have been ported to Drupal 8. This usually occurs within about 6 months of the release. There is alway the option to volunteer time or money to support any modules your require sooner than planned. As with any technology I use the rule of thumb to allow 6 months from initial release to ensure that it has been tested.
What about custom modules?
If you have created custom modules, you have 2 choices. Find a community supported replacement or pull out the checkbook and call a programmer to port or rewrite the custom module.
In short, the days of the build it and forget it website are long gone. The internet changes constantly, security is a never ending battle and your visitors expect to be dazzled by the latest bells and whistles while still being able to navigate your site with ease. So be sure to plan ahead and budget realistically to keep your website fresh and your visitors engaged.