Markdown allows you to specify links [like this], and then specify the link target later in the file:
This is really nice, and makes for very readable raw text, but it has a disadvantage when WordPress decides that it wants to automatically make an excerpt of something by truncating the raw text, then running it through the filter. You get a very ugly excerpt and lots of hanging links. The alternative, of course, is to process the text, produce XHTML, and then truncate it randomly, producing (probably) malformed XML. Not nice.
As a work-around, I’ve just removed all excerpts from this site – everything that ever appears should be full-text. It’s not like I type a lot normally…