I saw the following post on Facebook the other day and it really demonstrates how important it is to stick to standards on the web, and that nice URLs are far more user friendly.
Which of those links would you click on? If you chose the first you wouldn't have hit the page The Boileroom were hoping you'd see because the URL uses the | character which Facebook apparently doesn't think can be part of a URL.
Note how the second link is no more SEO friendly than the first, but it's definitely more user friendly. I think it's vital that website designers place as much importance on the URLs used on their sites as they do on aesthetic and SEO considerations. A clean, simple URL looks sharable; it won't put people off sending the link to their friends and it won't get broken by websites that don't cope with every valid character.
Think about how your URLs look, how they will be used, and make sure you design them so that when they get shared they look inviting and actually work, even with poorly written HTMLifier.
I also think that whoever posted this on Facebook needs shooting. Why didn't they immediately delete this post when they saw that the first link won't work and repost it using a URL shortener? Social media fail!