This is something I’ve been asked about blogs, Facebook, Twitter, etc. My advice is that you ought to keep a professional brand out there for your company.
I have two accounts, one for me personally (@way0utwest) and then one for my site (@SQLServerCentrl). The company site definitely gets less time from me than my personal account. I rarely sign on to the company account away from my PC, so it’s hard to maintain.
What I suggest first is that you use the company account to talk about the company, but make sure that someone is watching them. I would share this account with multiple people, and get them to spend a little bit of time each day posting items.
Feel free to retweet to/from your personal account and business accounts to the other. When appropriate. The important thing to remember is that the business account is based on your business and should match your business.
The personal account is for you, and you can get away with some tweets that aren’t business related, but if you are closely associated with your business, be careful about what you tweet. Remember it’s still your brand.