I put together a quick screencast that shows the power of Heroku and how easy it is to deploy your app in literally seconds. I've started moving all of my little sites there. My company is even going to try a few of our new apps on there to see how we like it for bigger things.
Heroku is worth checking out even if you're happy with your current host. Their architecture is really impressive and the add-ons are really cool.
At first my app gave me an error saying it couldn't load gems. I thought I needed to unpack my gems, but Heroku replied to me on Twitter and provided a really good alternative to unpacking!