Guideline 7. Ensure user control of time-sensitive content changes.
Section 508, (Technical Standards) 1194.22
http://www.w3.org/TR/WCAG10/#gl-movement
"Ensure that moving, blinking, scrolling, or auto-updating objects or pages may be paused or stopped."
7.1 Until user agents allow users to control flickering, avoid causing the screen to flicker.
7.2 Until user agents allow users to control blinking, avoid causing content to blink (i.e., change presentation at a regular rate, such as turning on and off).
7.3 Until user agents allow users to freeze moving content, avoid movement in pages. When a page includes moving content, provide a mechanism within a script or applet to allow users to freeze motion or updates. Using style sheets with scripting to create movement allows users to turn off or override the effect more easily.
7.4 Until user agents provide the ability to stop the refresh, do not create periodically auto-refreshing pages.
7.5 Until user agents provide the ability to stop auto-redirect, do not use markup to redirect pages automatically. Instead, configure the server to perform redirects.
I can't tell you how many of those annoying flash ads I've seen on various web sites that have the blinking button that says "Click Me" and you have to click it a million times per second so the cartoon Sumo Guy doesn't crush you. AGGHHH! Now luckily for me, I have most of those ads blocked, but I have ventured upon some pages that are seizure conducive environments. Black background, green and red text that flashes on and off. They are, to say the least, very annoying. Needless to say, I have never re-visited a site that uses strobe or blinking text effects. So what is the morale of this story? Don't make your webpages distracting and or annoying. If you do this, you will never get repeat visitors, oh yeah, and NO ONE WILL HIRE YOU TO BUILD THEIR WEBSITE!
I agree with most of this guideline, but for WCAG 2.0 I would like to make a recommendation to this guideline. Change guideline 1 and 2. Actually, they don't have to be changed, just get rid of the first part of the sentence that says: "Until user agents allow users to control [flickering, blinking ] avoid..". Change this so that it simply states: "Avoid making your site flicker or blink." Don't give me a control to stop it because odds are, I will be so annoyed with your site within the first two seconds, that I won't bother looking for a "Turn flickering off" button. I will simply leave your page, and blacklist it, never to return again. Redirects, auto-refresh and movement, such as an animation is not as bad as the first two things. Yes, they are annoying, but multimedia such as a flash movie can be deactivated and a redirects can be useful.
In conclusion: If you make your site blink, flicker or strobe, you will lose visitors. You may also cause a person to have a seizure, which could end up in a lawsuit. Avoiding lawsuits will help you save money, so please, obey this guideline.