Checking for broken links on my sites is one of the things I tend to forget to do. I bet most of you do as well. But it actually is important, not just from a user-standpoint, but from an SEO standpoint as well.
I have had Google ranking problems in the past simply because of broken links. Yes, I swear, it's true. Fixing the broken links made everything all happy again.
So, take some time today (or this week, if you really must procrastinate), and check those broken links. A quick way, especially for large sites, is to use Xenu, which can be downloaded here.