Man what a surprising bunch of uneducated crap I've been reading. Have any of you heavy criticizers installed it, learned how to develop themes, and gain a complete and full understanding of the WP core and the incredibly impressive Codex with a bajillion helpful functions at your disposal?
I've developed customized WP sites for things like realtors, business directories, news sites, restaurants, online stores, local governments, and quite a few small/medium sized businesses.
The only way to use WP to it's full advantage is to first of all, take advantage of custom post types and taxonomies. Organize your content. Also, you need to customize the backend so you're only allowing you client to see certain information. There are great plugins available such as Adminimize, and the User Role Editor for properly assigning permissions to your user roles.
As far as security is concerned, this obviously depends on the administrator. Simple things such as not using "admin" as the administrator, and NOT using wp-admin as your path for the backend, proper file permissions on the WP installation dir, etc, are all simple practices.
To say WP is just blogging software obviously means you haven't been paying attention for the past 3 years.