I'd personally like it user controlled, as many different sites have slightly different HTML restrictions - some you have to escape angle brackets within <code> tags, on PerlMonks you don't. I can't remember the correct syntax for the [id://node_id] or the ISBN tags, nor can I remember the &#091 and &#093 tags. Too many things to remember, but a little reminder at the bottom of the page would help sooo much.