I have to admit, I've long been an advocate of WordPress (above) but recently I saw the downsides all to clearly when I was contracted to correct a couple of issues with a WP install.
Essentially one of their staff had been hired with "WordPress knowledge" and had been given the task of setting up an online shop for an individual. They had gone off sick for a couple of days and the company couldn't get in touch with the developer so they asked me to quickly fix a couple of issues regarding layout and design.
However, being the diligent person that I am, I did a full scale review of the site to understand what I was working with. Essentially, it turned out, that in addition to having a whole bunch of regular security flaws and complete lack of best practices, they were sending credit card details across the internet without any encryption.
The site had been live for two months.
With the right knowledge WordPress is incredibly powerful, it can be used to create fantastic looking and functioning sites that are easy to maintain and are incredibly flexible.
Unfortunately, in the wrong hands (as I've seen on more than just this occasion) they can be a minefield of bad, and genuinely horrific, practices.
I've long held the opinion that setting up a website, without expert knowledge, can be hard and quickly become a mess. But to set up a website with WordPress without these skills can easily become dangerous.