Lots of people seem to have been inspired by Tim Bray's Doing it Wrong post just like I was. There's a great response on rc3.org titled "Do you want to be in the software business?" that expresses a lot of the same issues I raised in The Ruby on Rails CMS Dilemma.

The gist of the post is that you shouldn't commission custom development unless you're going to be "in the software business". If your custom software as intellectual property that is a reason for people to invest in your company, then by all means, build it custom. If it's not, then make due with whatever existing product best fits your needs. Just because you can, doesn't mean you should.