We just completed and lunached our site on wordpress after a dev time of about 1 week. Of course we had a great word press consultant in Bill Erickson of billerickson.com but I give more of the props to wordpress.
We went with The Thesis theme and we certainly are using WP as a CMS. In fact, I have just left, after only 3.5 months and enterprise cms software product that has over 20,000 installs. Plain fact is the user experience was terrible, the SEO was non existent and we had total vender lock, absolute prisoners if we wanted even the smallest change.
Our incoming search from keywords dropped from over 25,000 per month to about 500 per month. The stats were flatline.
I have come to know the inside of a cms very well and can say without hesitation the the UI and workflows inside wordpress are far superior then our last product which cost 50k to develop and 12k to license.
With words press, even in a short few days our analytic numbers have improved tremendously in all key areas, bounce rate, pages per visit, time on site.
The plugins we have have employed are simple but effective in creating a better experience.
I can endorse wordpress as a CMS without hesitation and only wish I had given it a look a few years ago. We could have been so much better off by now on our site, http://www.harvesteating.com
Keith