I'll never think of line delimiters the same way again. Mac uses \r, Unix uses \n, and Windows uses \r\n. Who cares? Well, when it comes to writing platform-independent Wiki markup, it matters.
Take for example a document that was written on a Unix platform. Every line is separated by a single \n character. For Wiki markup, paragraphs are separated by an empty line, which is represented in the document as two consecutive newlines \n\n. When a Wiki markup parser converts this document to HTML, it looks for the empty newline (the second \n) and uses that to close the previous paragraph and start a new one.
Now what happens if the document is opened and edited on a Mac? Mac uses \r as a newline. Suppose the Mac user adds a new empty line just before an existing one in this same document. For example:
Prior to editing:
some text\nmore text
some text\r\nmore text
Prior to adding the newline, the document contains a single \n character, and afterwards the document contains \r\n. In the users editor (on a Mac) the \r\n will appear visually as two lines, however \r\n happens to be a Windows line delimiter and thus will be parsed by Windows-accomodating Wiki markup parsers as a single line delimiter. In many documents this may not matter, however in Wiki markup this can make a big difference.
Editors that support editing Wiki markup on multiple platforms must be coded carefully to avoid this issue. For Textile-J this means that the end-of-line markers are converted to the platform default when the editor first opens a file.
Who knew that line delimiters could be so important.