Heroku is free. It's also easier and available right now. I uploaded the code for http://fuel.dustincurtis.com and it was working within 10 minutes.

For most of my little fun projects, I don't need an entire instance, and Solo is extremely expensive for that.

Also, I have a question for Engine Yard: why did you make the EC2 stuff transparent? One of the downsides of EC2 is that it has a very complicated pricing structure. The people Solo is targeting probably don't want to deal with a 20 row table of different prices.