I've added a Twitter account for openmikes.org, @openmikesdotorg.
No, you won't hear about what the site had for breakfast, nor will it show you pictures of its cat.
What it will do is tweet each time a new open mike listing is added. Each listing will be tagged with its city and state, so a search for #Los_Angeles_CA will let you watch for new LA listings. Each post is also geotagged based on the club's address, so you can do a location search near you if you'd prefer.