The golden rule every expert stress is that the corporate blog should not be another marketing space for your company. Then what goes there? At least it should not come to readers' attention that the company is marketing their own product. But some companies use their blog as a place for their press releases. Better to have a separate web space for that but if you want to include that in your blog then at least categorize posts related to product releases and promotions as something like press releases.
It is a good idea to have a dedicated personnel to manage the blog. For example take a company in UK and industry being technology. If they were a typical company their blog would contain anything related to technology, anything British, news from the company and it's products and promotions. First two categories are the best in my opinion as technology being the industry and the company being UK. Its not cool to promote your products via your blog. It should be the place where you socialize with your customers and potential customers, a place filled with resources and info of industry you are in. You should be building your own culture there. A place where your customers group themselves as community. Just like a facebook page. Feed back you get from your readers is free market research. So keep this in mind when choosing topics for the blog. By maintaining a corporate blog you'll also gain good traffic to your website and also you get a chance to promote your brand. It is your company's blog they are reading after all.
Business Blogs: use your sidebars effectively