I started using Joomla 3 years ago.
I decided using Joomla, the main reasons were: the community behind it, the capacity to have modules on top of a core engine that worked in a very stable way.
It took me a while to understand how it worked, how to manage it and how to live with the evolution of the different versions that they were coming.
I had to upgrade from 1.5 to 2.5, as so many people of the community, I decided to build the new web page from scratch and take the opportunity to enhance things. Good things: better look&feel, real multi-language, less touch on the code, and the community grew-up.
This was easy, the challenge during this year was to try to implement VirtueMart on top of the Web. 4 months trying to do it, but we found that some of the functionality still does not cover the requirements we want for our on-line store. So we decided to use Prestashop.
Positive thing: I learned a lot about how Joomla works, and I started to investigate about the next generation of templates.
Tablets, mobile phones have massively arrived to average consumer, and the reaction of the Joomla community is a wide number of new templates adapted for these devices: more image, different positions for the information, new look & feel, new usability rules… all under a common name: responsive design.
This response design is represented really by the Expose Framework: you have to install it to make these new generation templates work.
What about the fourth year?
The challenge is easy: migration to Joomla 3.0. I still want to work with 2.5 and wait that 3.x matures.