So it was really rather easy to get setup with a blog with heroku and ruby-slippers.
I've got a padrino/sinatra app for the root of the site and I wanted the blog to be a self contained site on a sub-domain for my blog, so after a little investigation by searching for a godaddy alternative on Hacker News I came across name.com
It seems like they are intuitive to use, so I thought I'd check them out. First thing was buying the domain which was relatively pain-free without a huge amount of distractions and attempted up-selling.
Then I added a domain to my blog heroku config like this:
heroku addons:add custom_domains heroku domains:add blog.polyglotsoftware.co.uk
And again to my main app config:
heroku addons:add custom_domains heroku domains:add polyglotsoftware.co.uk
Then I went to my config panel on name.com to setup the CNAME entries:
Voila, after a couple of minutes it was all working.