I do not like adding myself HTML tags or LaTeX commands to text while I write. Having to take care about markup while writing is disturbing and I cannot fully concentrate on writing.
Fortunately there are several tools that facilitate writing plain text with minimal markup.At the moment my favourite tool is txt2tags. It allows me to write plain text with simple markup rules even I can remember.
When I want to have a LaTeX source to produce a pdf, I run txt2tags. And if I want to publish the text as a Web page, txt2tags can produce me the necessary HTML.
There are several other lightweight markup languages available for Linux. More about them later.