Recs.
Updated
SpecsUpdate
Pros
Pro Easy access to lots of great dev tools
There's a large selection of great development tools available for OSX. The operating system itself comes bundled with a powerful terminal emulator, called Terminal. Additionally, Apple provides tools, like Xcode, an IDE that contains a comprehensive collection of tools for developing OSX and iOS software, for free.
Cons
Con Most software is closed source
For people who like to use open source tools for their development work, this may be a problem. There's plenty of advantages to open source software, one of which is the ability to tinker with and customize the tools themselves that you are using. Although there's plenty of FOSS tools available for Mac, especially through Homebrew, the number of packages available is much lower than the number of packages available for any Linux distribution.