Mr Savage and Shugo Maeda have released ruby-prof 0.4.0. I have to admit that I have not had much need for a profiler in Ruby (For Rails or otherwise) so far but it is nice to know that there is a decent profiler available when, and if, I need one.
The addition of a call graph report is absolutely vital and having them in a cross referenced HTML report is pretty sweet. I have used call graph profiling reports in the past but it was always with plain text reports. Following a call path in a plain text report can be little tedious at times. I expect that being able to follow links to particular call would make things quite a bit easier.