Just bear in mind that the SaaS Rails Kit has been around for quite a while. I don't know if the features page lags behind the actual code, but: "Compatible with Rails 2.3.8"
I enquired the other day about Rails 3 support - he's working on it and expects to release it in the next few weeks.
In fact the rails3 release is mostly ready. There's a rails3 branch in the customer git repo that will be merged into master in the next week or two.