Passive Voice Is Redeemed For Web Headings (Jakob Nielsen's Alertbox)
The article has some great tips about not only SEO but also on people scanning SEO results for something to read and to scratch their itch.
The basic idea is that in user testing previously, it is almost always better to use an active voice (X does Y to Z) rather than a passive voice (Z has Y done to it by X) because it does not force the reader to think as much to figure out what is going on.
The difference comes in situations where only the first few words are going to be scanned, and where you need the most relevant terms.
It's worth taking a look at the article and thinking about when writing headlines for your blog. The article provides some specific examples that make it pretty clear what it is talking about.