A little research turns up that a more accurate translation would read "bitter greens", not "bitter herbs." The Israelites were instructed to consume this, along with the roasted lamb & unleavened bread, for Passover. This continued to be the arrangement for all future Passover celebrations as well. And though it's not specified which bitter herbs, or for what reason, many take it to be as a reminder to the Israelites of the bitterness of Egyptian bondage.

But ya know, I'm more in mellow's camp anyway. Even if the Bible came right out & said to roll a big'un, um... well, it's a book written by men anyway. Some boring, some actually very wise, & some confusing (hello Revelation). But ya know, it was still written by a bunch of common men, so why take it so darn seriously to begin with?