Not every company is going to want to use twitter for their tech support or announcements but because the service is so popular many have started accounts.
Others actually rely on it.
Here are a few companies that Use Twitter.
If you know of any more please add a comment with a link to their company website showing their twitter account. Please don't just list the Twitter account.
Firefox http://twitter.com/firefox_answers
GoDaddy http://twitter.com/GoDaddyGuy
QuickBooks http://twitter.com/quickbooks
Sun Microsystems http://twitter.com/SunBlogs
Cisco Systems http://twitter.com/CiscoSystems
HP News http://twitter.com/hpnews
