One thing that is particularly frustrating with caring about Web standards and accessibility is what often happens after your work is done and a site is handed over to the client.
I’m sure most of you have been there. Despite your hard work to educate the client’s editor(s), regardless of the style guide you wrote, and no matter how much time you spent patching the CMS they use, there will be problems.

456 Berea Street: Helping your client maintain markup quality