This post concentrates on some of the advantages that should impress and urge you to upgrade to Drupal 7. Drupal 7 was released on January 7, 2011, and it is a great accomplishment over the improvements of Drupal 6. So, just take a look at some of the most prominent improvements:
1. Superior Usability, UI and UX
An entirely refurbished and reinforced administrative interface makes routine tasks simpler. Many improvements have been added especially for the site builders and content editors. This includes the new Dashboard, with an easy and powerful drag-and-drop interface that can be customized by site administrators to include recent content, comments, content that require moderation, or any other block available to your Drupal site.
i. Administrative Toolbar
Top Admin Toolbar access can be set via User Role, and only the functionality permitted to that Role will be available from the toolbar.
ii. Shortcuts Drawer
Shortcuts may be general (a link to a Blocks page) or as specific as you like (a link to a specific view while you're still refining it). Also shortcuts can be saved as sets, making it possible to create one set of shortcuts for a Site Editor, another set for administrators etc.
iii. Contextual Links
Contextual links is the wrench icon that the administrators see when they hover over the various pieces of content. These provide a useful cheat-sheet for Drupal amateurs who may not know the source of the content that they are trying to edit. After editing and saving, Drupal gets back to the original screen.
It also includes refurbished Taxonomy setups, which facilitates adding images, descriptions and fields to content categories, and even add links to them. This is useful for heavyweight content sites and in theming, where a default image could be used to denote every piece of content in a specific category.
2. Enhanced Flexible
Drupal 7 allows you to define your own content structure and custom fields to content, users, comments and much more, without having to add modules. Apart from creating custom text and list fields, you can also upload images directly into the Drupal fields and create custom Image Styles to automatically crop and scale your images.
Drupal 7 now supports various databases such as, MariaDB 5.1.44+, MySQL 5.0.15+, PostgreSQL 8.3+ and SQLite 3.x+. As a result you get more flexibility and control over your site's data.
3. Enhanced Scalablity
4. New Core Themes and improvements
Drupal 7 also includes a hole host of new default themes, including:
i. Bartik: The Drupal 7 default theme, which is a clean, multi-region theme that allows easier customization of colors, regions and CSS style settings
ii. Seven: The D7 administration theme, a minimalist theme used in configuration overlays and administration pages.
iii. Stark: An entirely empty theme that provides a way to look under the hood at Drupal's default markup. This is helpful for module and theme developers who need to see the markup that Drupal is giving prior to their work.
5. Security and Testing Improvements
Drupal 7 comes with a number of important security improvements, some of them are as follows:
i. Password hashes are salted (passwords cannot be cracked with a look-up table).
ii. Unique Key for cron.php to make Denial of Service attacks more difficult (It cannot run by simply going to example.com/cron.php like you might be used to).
iii. Permissions have normal, human-oriented names and descriptions.
iv. Facilitates choosing between public and private files on a per filefield basis.
v. The Test module, which was formerly known as Simpletest is included in the Drupal core now. This module helps you to write tests to ensure that your site and the modules work properly, and also test your site after you make the changes.
Hope, that these changes or rather improvements of Drupal 7, are reasons enough for you to upgrade.