I first got introduced to it because They Might Be Giants wrote a soundtrack for Issue #6.
Issue #7 was a metabook. It had lots of little little books held in one big binding with a ginormous rubber band holding the thing together.
Issue #8 is dedicated to truth, lies, misdirection, etc. It has a hoax written by the well-known host of a Nabokov (author of Lolita) web page, and then that author's comments on his audience's reactions. There is a seriously wacky collection of snippets on the local customs, flora, and fauna of some nonexistant country. McSweeney's is orders of magnitude better than anything else out there and I would seriously recommend it for anyone who likes to read.