Being new to OS/X, my first concern is a usable terminal. Here are a few tips...
iTerm2
Apparently, Apple's terminal app really sucked in a previous life. It's better now, but iTerm2 had a head start. One of the most useful features is "mouseless copy," i.e., copy by highlighting, which will be familiar to all Linux users. Other neat features include the exposé tabs and search capabilities.
Fonts
Monaco is good. Other popular options are Inconsolata and Source Code Pro, a monospace relative of Source Sans Pro.
Color Schemes
Solarized is available for iTerm2 and vim. Here are other options.
Mind Blowing
The potentially awesome feature of iTerm2 is tmux integration! You can attach to tmux sessions, and have their windows treated as normal tabs. It is a killer feature. A special patched version tmux is required, and it has plenty of drawbacks, but it's new. I've used screen over tmux in the past, but this could be worth the change.
