We'll respond shortly.
"Has anyone used Unicorn"
No one present is using Unicorn. Some wondered how it differs from Thin.
This raised the question:
"Is there a road map for mongrel and rails? Mongrel uses CGI and Rails 2.3 has removed CGI."
In the Ruby on Rails 2.3 Release Notes, there is the statement
...but if you use CGI, don’t worry; Rails now supports CGI through a proxy interface...
Selenium removes the If-Modified-Since header. This gets in your way if you are testing ETags.
Speaking of ETags - they are awesome. See Ryan Daigle's article for code.
Just how slow is Mongrel when serving static images?
The answer is - pretty slow. The reason for the question was that Google's crawler tends to keep a single connection open and fire lots and lots of http requests over a period of several hours. With a standard Nginx/Mongrel setup, this would tie up a mongrel for this entire period.
A proposed solution to this problem is to use HAProxy between Nginx and Mongrel.
"How big should a typical mongrel be? Ours is starting out at over 200 megs but is not leaking from that point."
Everyone agreed that 50MB to 70MB is standard and anything over 100MB is considered pretty big. People suggested RubyProf for inspecting object counts and possibly tracking down the memory hogging code.
"What pattern does everyone use for non-model Reports with ActiveRecord? We are trying to create a report that counts a single model and groups by two associated models"
There was consensus around modeling a distinct report object and calling the referenced models. For example, FooReport and FooReportController fit nicely in a RESTful Rails world.