Is there any reason to go to Drupal 6????

In my opinion, there is absolutely no reason to switch to Drupal 6. I still use 5.9 and it is rock solid, and it works with all the modules I need. Every time I make a site in Drupal 6 I find that at least 3+ modules that I need only work for 5.x, and I end up switching back. And many of the new features of D6 can be obtained through modules. So no, there's no reason to use Drupal 6.

Drupal core is a foundation. Every change noted below was made for legitimate reasons. Major changes to the foundation require changes to contributed modules. If you want the contributed modules to be updated more quickly, you should consider contributing to that process. Meanwhile, feel free to use any version of Drupal that you wish.

Drupal 6.0, 2008-02-13
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- New, faster and better menu system.
- New watchdog as a hook functionality.
* New hook_watchdog that can be implemented by any module to route log
messages to various destinations.
* Expands the severity levels from 3 (Error, Warning, Notice) to the 8
levels defined in RFC 3164.
* The watchdog module is now called dblog, and is optional, but enabled by
default in the default install profile.
* Extended the database log module so log messages can be filtered.
* Added syslog module: useful for monitoring large Drupal installations.
- Added optional e-mail notifications when users are approved, blocked, or
deleted.
- Drupal works with error reporting set to E_ALL.
- Added scripts/drupal.sh to execute Drupal code from the command line. Useful
to use Drupal as a framework to build command-line tools.
- Made signature support optional and made it possible to theme signatures.
- Made it possible to filter the URL aliases on the URL alias administration
screen.
- Language system improvements:
* Support for right to left languages.
* Language detection based on parts of the URL.
* Browser based language detection.
* Made it possible to specify a node's language.
* Support for translating posts on the site to different languages.
* Language dependent path aliases.
* Automatically import translations when adding a new language.
* JavaScript interface translation.
* Automatically import a module's translation upon enabling that module.
- Moved "PHP input filter" to a standalone module so it can be deleted for
security reasons.
- Usability:
* Improved handling of teasers in posts.
* Added sticky table headers.
* Check for clean URL support automatically with JavaScript.
* Removed default/settings.php. Instead the installer will create it from
default.settings.php.
* Made it possible to configure your own date formats.
* Remember anonymous comment posters.
* Only allow modules and themes to be enabled that have explicitly been
ported to the correct core API version.
* Can now specify the minimum PHP version required for a module within the
.info file.
* Dynamically check password strength and confirmation.
* Refactored poll administration.
* Implemented drag-and-drop positioning for blocks, menu items, taxonomy
vocabularies and terms, forums, profile fields, and input format filters.
- Theme system:
* Added .info files to themes and made it easier to specify regions and
features.
* Added theme registry: modules can directly provide .tpl.php files for
their themes without having to create theme_ functions.
* Used the Garland theme for the installation and maintenance pages.
* Added theme preprocess functions for themes that are templates.
* Added support for themeable functions in JavaScript.
- Refactored update.php to a generic batch API to be able to run time-consuming
operations in multiple subsequent HTTP requests.
- Installer:
* Themed the installer with the Garland theme.
* Added form to provide initial site information during installation.
* Added ability to provide extra installation steps programmatically.
* Made it possible to import interface translations at install time.
- Added the HTML corrector filter:
* Fixes faulty and chopped off HTML in postings.
* Tags are now automatically closed at the end of the teaser.
- Performance:
* Made it easier to conditionally load .include files and split up many core
modules.
* Added a JavaScript aggregator.
* Added block-level caching, improving performance for both authenticated
and anonymous users.
* Made Drupal work correctly when running behind a reverse proxy like
Squid or Pound.
- File handling improvements:
* Entries in the files table are now keyed to a user instead of a node.
* Added reusable validation functions to check for uploaded file sizes,
extensions, and image resolution.
* Added ability to create and remove temporary files during a cron job.
- Forum improvements:
* Any node type may now be posted in a forum.
- Taxonomy improvements:
* Descriptions for terms are now shown on taxonomy/term pages as well
as RSS feeds.
* Added versioning support to categories by associating them with node
revisions.
- Added support for OpenID.
- Added support for triggering configurable actions.
- Added the Update status module to automatically check for available updates
and warn sites if they are missing security updates or newer versions.
Sites deploying from CVS should use http://drupal.org/project/cvs_deploy.
Advanced settings provided by http://drupal.org/project/update_advanced.
- Upgraded the core JavaScript library to jQuery version 1.2.3.
- Added a new Schema API, which provides built-in support for core and
contributed modules to work with databases other than MySQL.
- Removed drupal.module. The functionality lives on as the Site network
contributed module (http://drupal.org/project/site_network).
- Removed old system updates. Updates from Drupal versions prior to 5.x will
require upgrading to 5.x before upgrading to 6.x.

Just because you need CCK or LDAP etc doesn't mean everyone else does. There are hundreds of other modules that are available for Drupal 6.

OK, if you need that stuff then that's fine. Just use 5 - no big deal, the modules you want will catch up if there is enough support behind them.

Before you complain about Drupal 7 stealing your precious gurus - are you sure that your modules are being held up by the module authors doing core development instead? Or would you want those that are doing core development to drop everything to work on the modules you use instead?

As for what is new and better than 5? Drupal 6 offers a lot more flexibility and power for module and theme developers which will eventually trickle down into the modules and themes that are available. eg Views2 and the devel modules theme development enhancements are just two examples of functionality that would be much more difficult to implement on Drupal 5.

--
Anton
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The new Views module is really nice, Views 2. Some really nice features. I spent a few hours weighing this decision, and I chose not to upgrade to 6. I will most likely go from 5x to 7x, and totally skip out on 6.

However, if you are new to Drupal I recommend you go ahead and start with 6.

D6 has around 4 or 5 features over D5 that makes it a neccessity for me. I was never able to get my site to work correctly in D5 like I wanted it to, and suddenly D6... It was like seeing God. But anyhoo, your needs are different from mine, do whatever works for you. But you should recognize that some people actually have a need for d6 that's beyond the bigger number.