Great comments. It is not so much about specific word count as staying relevant and on point. I learned a good rule of thumb years ago - write your blog, set it aside for awhile, come back and cut it in half. I find it works exceptionally well. I just cut two sentences out of this commentary and the message did not suffer for it.
In addition, keep in mind time constraints of your reader. Your goal is to have your blog read now, to provide inspiration and dialogue. If its length dictates later review, it might need some condensing.