Write a jQuery plugin that makes an element act like a <blink> tag. It should work for any arbitrary speed.

http://learn.jquery.com/plugins/basic-plugin-creation/

Make plugin work for selectors that correspond to a single element.

// show/hide every 1000ms
jQuery('.myDiv').blink(1000);
// twice as fast
jQuery('.otherDiv').blink(500);

Make plugin work for selectors that correspond to multiple elements.

jQuery('div').blink(1000);