There are many improvements to enjoy in Joomla 3.
One small but highly useful improvement is the new sample data. Honestly, in Joomla 2.5, the sample data wasn't good at all. Because it was so confusing, we recommended that our students avoid using it.
With Joomla 3, you have 6 different sample data options, and almost all of them are useful. When you get to the final step of the Joomla 3 installation process, you'll see these 6 options:
Option 1: None
This is the simplest of the 6 options. Joomla will be installed with no menu links, no content and no modules.
Option 2: Blog English
The Blog option will set your site up in a typical blog format. There will be articles published on the homepage with a read more link underneath. You'll also find several modules in the right-hand column including a list of recent posts, a blog roll, and a list of most popular posts.
Option 3: Brochure English
The Brochure option is designed for company website. It installs with a static homepage, plus About Us, News and Contact Us links in the menu.
Option 4: Default English
The Default English option is probably the least useful. There's only a single article and that's published on the homepage. It is very close to simply being the same as Option #1.
Option 5: Learn Joomla English
The Learn Joomla option is the same as the sample data for Joomla 2.5. There is literally an example for every single extension and template that is installed with Joomla.
Option 6: Test English
The final option, Test English, is designed for people who are helping to test Joomla 3. There are examples of all the layouts and components you might want to test. The homepage is taken up with a detailed article on how to start testing.