Using ruby-prof to optimize rails apps


I have some apps that need a bunch of tweaking and optimization and
I’ve been messing with ruby-prof, seems like the best way to go.

Anyway, I would like some suggestions from people as to the best way
to use this tool? One of my main questions is, there seems to be 3
major ways to profile: starting an application with the ruby_prof
executable, explicitly stating which chunks of code to profile, and
including unprof to just profile it all. What could be better?
Starting webrick / mongrel with ruby_prof, or the two other options
within the rails app?

Does anybody have any other suggestions?