A pretty similar design was my first try for a simple whiteboard system but switched to another misuse of memcahced with prepend and append. Timing out of old messages is a nice feature of this solution. These are dirty hacks comparing to a "proper" solution but sometimes they are OK enough.

Beanstalkd has a memcached like protocol but designed for simple queues. It's a fine system but I'm missing the timeout feature. http://xph.us/software/beanstalkd