. . . open source content management application on the web, their stats and websites that use it prove that. Have a look at their website on www.wordpress.org to form a personal opinion.
If you have a busines to run and have limited time - do you really read all their content before getting into it? It was a long read for me and as I write this post am a bit reluctuctant to use it- there seems to be a lot to know, especially if you're not tech savvy and realize the internet is one of your bases for marketing. On the one hand open source is great but it seems you need spend a lot of time reading through stuff and having someone implement it for you anyway.
It sort of takes away the fun of having done every single function in your comany including the website. When I have 4-hours to read, probably another day to implement Wordpress and some time to read through their forum regularly - I look forward to doing it. It just wont be soon though.