The txt2tags user Huahai wrote a very nice article about txt2tags. In a few words, he/she (sorry!) gave a complete overview of the program, speaking about its advantages among other formats and about using it as a GTD tool.
“Speaking of portability, plain text is without question the king. So, when we need extra features, such as structure, list, table, links and so on, we add them on top of plain text. The question now becomes how much to add? Many formats trade power over simplicity. For example, LaTeX is great, many people I know write papers with LaTeX, myself included. However, LaTeX is too complex for quick text entry. Wiki is great for documentation, but there are just too many different kinds of wiki tags for me to remember. Here, I think txt2tags strikes the right balance between power and simplicity.”
“For quickly jotting down ideas, I have tried mind-mapping tools (freemind, kdissert), outliners (TVO, vimoutliners), and note-takers (basket, knotes). They work to some degree but are all very limited in term of content expandability and portability. I just wish I had found txt2tags earlier.”
Read the full Huahai article: txt2tags: a Lightweight Document Authoring Format