Works great. Operational limit: 524,287 characters ... any idea why it dies at 2^19? I guess it's probably 'count's data type.
Pretty Cool stuff! I especially like the comments :)
Sam, I think the length limit is imposed by the browser as a limit on the length of a single <input type=text>. Had I used a <textarea> instead, this limit would probably be higher, and I'm sure this varies between browsers.
In a recent Firefox build I got up to "You entered 2097152 characters." before stopping testing. (Hold down Ctrl and hit A C V V to double the length of the text.)