ssh-agent under OSX
Get ssh Login to start an ssh-agent that's inherited by all of the terminals you start on the desktop. Then you type your passphrase once when you log in and all further ssh authentication is handled by ssh-agent.
Newlines
The three major computing platforms managed to come up with three different conventions about newlines in text files. This is particularly annoying in OSX since different applications are following different conventions. Here's a Answers/Code/NewlineScript to convert between the three formats.
You'll find yourself in Nirvana if you use this within Emacs: You're looking at a buffer with wonky newlines. Highlight the text and type "M-x shell-command-on-region", then "rets m u" to convert from the Mac convention to the Unix convention. Ta-da! The text is now nicely formatted in a new buffer.
Xload under OSX
The port of Xload to the Darwin kernel is completely brain-dead. Rather than averaging over the past few system load measurements, Xload just plots the instantaneous system load. So, when I open up my iBook and all of the idle processes are briefly woken up before deciding that they can safely snooze again, the system load shoots up to five or six. But only for a few seconds. This results in a large spike in the Xload display. Silly. Here's an Answers/Code/XloadPatch to fix it.
Dropscript
You should know about DropScript, which wraps some OSX fluff around a shell script so that you can drop files onto the icon and have the shell script do something to them.
The syntax is a little wacky since OSX filenames can have spaces and such, so here are two Answers/Code/DropscriptExamples.