Are the techniques presented in chapter 8 "Dealing with Success" specific to RESTful Rails?
I would assume that REST may only add value to scaling due to the stateless approach; something like stateless session EJBs. On the other hand scaling techniques specific to REST may be still premature.
In general, the tactics I discuss aren't specific to REST or to Rails. Scaling a Rails application - RESTful or otherwise - is much like scaling any other application: minimize the cost of each request, etc.
A truly RESTful system would make this a bit easier, but it wouldn't eliminate the problem entirely - statelessness, for example, wouldn't help much if your application churns away for five seconds on every request.