Susan Mernit posts about the “just jump in” corporate blogging philosophy. I tend to think that corporate blogs should, at least, have an idea of their editorial mission and scope before just jumping in. It’d also be helpful to have a solid handle on the blogosphere, so you could learn from others’ mistakes.
And folks should understand it’s a big commitment. One thing I find with writing is that it takes training and practice to be able to meet a deadline — to write quickly and succinctly and coherently. Blogs, by their very nature, have daily (at least) deadlines, and you don’t want to get into a “writer’s block” situation. My husband, for example, has drafted out probably 1000 words for an entry in his blog, but he still hasn’t made post one. Even people who write professionally (but not under constant deadline pressure) can find it difficult to write when there’s a deadline.
So perhaps when it comes to planning your blog, think twice and take your time. But when it comes to the writing, just jump in.