Just wanted to chime-in with my K2-powered site:
www.cristoreyjesuit.org
A year ago, I designed the site using Joomla, and a modified template from RocketTheme. About three months ago, I began looking at redesigning the site. I was looking for something that was easier to update, and generally worked "better" than the out-of-the-box Joomla install. I spent some time playing around with Wordpress, and then looked at maybe doing a total redesign of the site . . . in the end, I decided to give K2 a shot and I've been pretty happy with it. I figure I'll re-evaluate the CMS situation when Joomla 1.6 comes out. Until then, I'm going to stick with K2.
I'm just using K2 for the news section -- I've turned off a lot of the features like comments and ratings. I did a lot of tweaking/editing to the CSS and PHP to match what I was looking for. The big thing I'm struggling with now is that I'd like to find a better news rotator for the front page. I'm waiting to see what else becomes integrated with K2 -- right now, nothing was quite what I was looking for, so I'm sticking with RokTabs.
Other than that, just wanted to say "THANKS!" for such a great Joomla component. I'm really, really glad I made the move to K2, and I can't wait to see more and more sites using it.