you would might want to consider a close group of people in your company beside a person who will write content to propagate topics and content ideas, as well as reviewing the content that is about to be published in order to see if it stretches established security boundaries and such.

By going online you have several risks, and some rewards. You mentioned one of the most mentioned risks there is: competitors stealing ideas, and knowing what you're up to. It's a risk you'll have to deal with, I think. If it's you personally who's gonna do the writing, you'll have to get the idea of when is enough. A blog is a great tool, to get feedback, and to share with others your company's plan. Problem is, when one knows, everyone knows.

You should talk to your customers and to your target audience.

They want to know about what you are doing for them, what products are you launching, or what services you are coming with.

They do not want to know how profitable is each product or how much you made in Q3.

Use an informal voice, with serious content.

Your blog is a great way to comunicate with your customers and get feedback from them. Comments from your customers are addressed at you, so probably your blog won't be as useful for your competition to peep as it will be for you as a communications channel.

The key is to take control of the conversation you're starting. Create a strategy, make a plan. You won't walk on the street and start yelling company secrets right? Ok, the same goes on the blog.

Generate ideas, create value, a development blog is just another face of your company. GnrlBzik has something when he writes about a group of people. You shouldn't be all alone writing on the blog. What I like about those types of blogs is to hear different voices, not a single tone.