Vim comes with OS X by default, but it doesn't come with X11 support. You can always install MacVim of course, but some of us prefer to use vim in the terminal. Unfortunately, because of the lack of X11 support, copying/pasting doesn't work correctly in OS X.
As an example, copy a paragraph of text from Safari, then paste it into your vim instance in the terminal. Chances are, if options such as AutoIndent are on, the paragraph will be rearranged.
On Linux, we have the + and * buffers for that. That way, a simple "+p command will paste the most recently copied text into the terminal version of vim.
To enable this on OS X, I added a hint to my Vim page.