Some domainers and domain companies use Twitter effectively and some don't care much for Twitter. Registrars like Namecheap with over 100,000 followers use Twitter effectively and give back to the industry and their non domainer clients by running contests that give away free or discounted domains.
Name.com (an advertiser) also does a good job communicating with their clients and offering discounts and the latest news on their promo codes. Name.com does also look to add some comedy to their tweets as well.
DomainMonster is up all early every day tweeting away and greeting their "monsters", the Lady Gaga fans may not appreciate the monster moniker as they are one of the largest groups on Twitter.
Twitter can be an effective tool for domainers if the account stays on point, followers look for info or quotes or domains for sale. Some domainers tweet about closing sales and other industry data.
Zendesk put together an informative look at just how small business is using Twitter. Hopefully it will provide some insight for those looking to improve their Twitter reach to grow their business.