Yes I am using Mac OS X (ATM snow leopard ak 10.6) on my MacBook Pro. I've to admit that I am not a big Mac OS fan and my work flow is much smoother on linux. But Here is a short list and description of software I am using and configuration steps I've done. (just to document them and to not forget them - perhaps it's also interesting for somebody else)
Software
iTerm: That's the terminal program of my choice. I don't think I've to explain to much - it is pretty simple but yet powerful.
MacGPG2: is an allready bundled and working gpg distribution. It provides you with the gpg-agent and a mac os tool to enter the passphrase.
Thunderbird: I am using Thunderbird (and not Mail) because I am used to it. I've tried Mail and it's not bad but I am slower and I'd need a second configuration. As interface to gnupg I am using eingmail. At this point I've to say once more that I'd use mutt if people would realy use eMail for communication and not to send eye candy.
Firefox: The reason for not using safari is (and I think that's for a lot of user the fact) the possiblity to use add-ons. I am using
- Firebug
- Xmarks (I am syncing my bookmarks against my own webdav)
- Texto (the successor of mozex)
and I am very used to them.

git: is the version control system of my choice. This google code project provides you with a really usable compilation.
Aquamacs: I really need emacs. We are using the "operating system" Mac OS only to start the "real one" - emacs - aren't we?
(BTW - Aquamacs doesn't mean that this is based on the aqua API. Todays releases are all based on the cocoa API)Zsh: I am using zsh and I love the config from the [grml][grml] distribution. Simply download the
.zshrcwithcurl "http://git.grml.org/?p=grml-etc-core.git;a=blob_plain;f=etc/zsh/zshrc;hb=HEAD" > .gitrcTo change the default shell you can go to "System Preferences" -> "Accounts" -> right click on your username -> "Advanced options".
[StuffIt][stufit]: Has prooven itself to be a usefull unpacking utility
Configuration issues
Using CapsLock as second "ctrl": Since 10.4 it couldn't be easier. Go to "System Preferences"->"Keyboard"->"Modifier Keys" and do what ever you want! (I had a realy bad emacs pinkie but now I feel much better)
Speed up keyboard: You can stay in the keyboard setup as described in the last tip. Move the slider for the "repeat rate" and the "delay until repeat" till the right. I don't know what's the matter with the people at the infinity loop - but the default settings are soooo slow.
That drives me crazy!
- Have you found a cute solution to use the "option" key as "meta" inside of iTerm? Especially if you are connected to a linux screen session inside of iTerm through ssh. The whole key mapping issue between mac and linux drives me crazy. I can't override "option" to be "meta" because else it is impossible to get the whole "[]|{}" crap. Aquamacs has this magic " ... Meta & German" hack - perhaps there is a possiblity to learn iTerm something similar?