There's always debate on the net about who you should allow to blog and speak for your company.  Mark Cuban is an extreme, but he does not allow anyone within his organizations to blog since he wishes to be the sole voice of the company.  Personally, I think this probably hurts him more than helps him.

Other companies put their Marketing team on it, so the content is really regurgitated site content, whitepapers and case studies.  The verbiage is refined with little personality. Blah... blah... blah... Zzzzzzz...

I think Chris Baggott nails it when he says that the best company bloggers you have are the people that are closest to your customers.  They understand the relationship between your products and services and how it assists their business.  They also understand the challenges and successes.

When you wonder about who will be a company blogger, you should ask yourself who you'll entrust your clients to?  Who will be fulfilling your business relationship?  Since blogs provide such a rich quantity of qualified leads through search engines, it's typical that the search engine user is asking the exact question that your employee can answer.  Not your CEO, not your President, not your VP of Marketing... but the person who you've entrusted the relationship with.

That means that you can assume a pattern where your employee who handles the customer will write about topics important to the customer... which, in turn, will be topics important to a new visitor!  As a result, customer-facing employees happen to make fantastic company bloggers.