I’m an ex *nix admin, so I ‘get the drift’; however, I’m
looking for a good guide to OSX to help the transition. Not
so much a ‘dummies’ guide on how to organize the family
photos, but something outlining idiomatic usage for
productivity-intensive use such as software development.
Welcome to the cult. 
I’d be interested in hearing from others, too, but I don’t think you’ll
find so much as a complete idiomatic guide but rather, good advice in
bits and pieces relevant to your specific needs.
One thing that really helped me was the O’Reilly’s “Mac OS X for Unix
Geeks” that Ray mentions. I know you’re an experienced *nix admin but
OS X is a little different from the usual *BSD directory set-up and it
also differs in user management and with service/daemon management
(launchd is awesome!). Additionally, there are Mac OS X-specific BASH
commands like ‘fs_usage’ and you can find a pretty complete list here:
www.ss64.com/osx
Another example of how Mac OS X is a little different: it’s generally a
good idea to edit Apache’s httpd.conf file in:
/etc/httpd/users/your-use-name.conf
…instead of /etc/httpd/httpd.conf to be “upgrade safe” although both
files are there.
For setting up your Rails and/or web development environment,
www.hivelogic.com is a pretty good source as is
www.entropy.ch/software/macosx. And of course, all technically-inclined
Mac users should read daringfireball.net.
And finally, if you have specific questions, the other folks on this
list will no doubt have some good advice for you.