Permalinks
Permalinks are called premalinks because they are, or should be, permaneant. If something is going to be permanent on the web(well, everything on the web is), you want them to be meaningful and pretty.
By meaningful, I mean permalinks should include a published date or some kind, and a slug. By pretty, I mean no unnecessary clutter. The following is my ideal permalink format for a blog post. (I chose to include the 'day' in the permalink, due to an implementation detail).
http://yak.limelog.net/2012/01/02/permalinks/
That's much better than this:
or this:
http://limelog.net/post/11091170754
They are also what guides people to your website. People should be able to expect what kind of content they will recieve just by looking at the URL. That's why I dislike the act of URL-shortening. You never know what you're going to get. If it needs to be shortened, then someone's doing their job wrong.