I’m using K2 to my Multilanguage Joomla 2.5 Website with 2000 articles. It’s working very nice and it has all the missing features that Joomla content doesn’t. I really like the tag system, the way it handles the categories especially the inherit parameter. The extra fields have limitless possibilities! The only con is that it gets a little bit slowly to load with some articles. K2 is probably the best open source CCK for Joomla and the best thing is that it is supported by many Templates and has lots of 3rd party plugins.