It's a trick question. I'm not sure there are any highly effective bloggers. ;-)
OK. I might possibly concede there are some effective bloggers, but I think there are a lot more successful, ineffective bloggers than there are effective ones.
So what's the difference? If effectiveness is having a lot of subscribers, then there are a lot of effective bloggers. If it's having a bevy full of commenters who disagree with you, then there are a lot of effective bloggers. If it's richly expressing yourself, then there are a LOT of impressively effective bloggers. I applaud all those things, but in my opinion those are measures of success, not effectiveness.
An effective blogger is one who has achieved synergy with his/her commenters. Together they are meaningfully wiser and more capable than they could be apart.
Now, I know that sounds easy, but it's not. Covey's 7 Habits was a smash hit, and for good reason. It sets a high and useful bar for the idea of what's effective. I might be wiser because of a comment on one of my posts, or a reader might be wiser because of something I said. Those are certainly effective moments, but moments like that fall way short of synergy. Take a look at Covey's habits 4-6:
+ Habit 4 - Principles of Mutual Benefit: An attitude whereby mutually beneficial solutions are sought that satisfy the needs of oneself as well as others, or, in the case of a conflict, both parties involved.
+ Habit 5 - Principles of Mutual Understanding: Covey warns that giving out advice before having empathetically understood a person and their situation will likely result in that advice being rejected. Thoroughly listening to another person's concerns instead of reading out your own autobiography is purported to increase the chance of establishing a working communication.
+ Habit 6 - Principles of Creative Cooperation: A way of working in teams. Apply effective problem solving. Apply collaborative decision making. Value differences. Build on divergent strengths. Leverage creative collaboration. Embrace and leverage innovation. It is put forth that when synergy is pursued as a habit, the result of the teamwork will exceed the sum of what each of the members could have achieved on their own. "The whole is greater than the sum of its parts."
These are the "Independence to Interdependence" habits and build on the "Dependence to Independence" habits. I think blogging really suits the first three habits wonderfully, and maybe the 7th habit, but I don't think many bloggers have really achieved interdependence. I'm not sure they can.
I can imagine interdependence working in the blog world, but not very easily. It takes my most optimistic and idealistic dream state to really picture it. I'm sure opium would help with that. But opium or not, I don't think imagining it is going to make it happen (no apologies to John Lennon - the dude was way wrong.)
We bloggers are too ethereal to support deep relationship - strong relationship sometimes, but never full-bodied.
You never have to put up with my bad breath. You can skim/ignore my tennis posts. You can ooh and aah when I get something right and quietly ignore (or loudly protest) my errors. You can picture me with red hair or a pleasingly Benedictine demeanor. Whatever images drift lazily across your consciousness as you read my words, they mean only what you perceive them to mean. I relate to you as whatever your subconscious assumes me to be, and it's impossible for you to see me any other way. You're kind and optimistic people, so you almost certainly see me as better than I really am (and I appreciate that) but I am assuredly different from your subconscious picture of me. Only a handful of verbal slivers of Kevin Knox are real to you, and the more we attempt to overcome that unreality, the more we're just spray-painting a ghost.
I cannot commit myself to people who vanish simply the moment I unsubscribe from their blogs and delete their emails. I can only commit myself to people who are still there, week in and week out, no matter how badly they frustrate me. It's only in the daily grind I can really learn whether they're trustworthy. Via the Internet I can share a mutual commitment to Christ with anyone in any corner of this wonderful globe, but I can only interdepend with people who've seen the real me - with people who will soon have to forgive me, because they can't just change the channel and make me go away.
It's only the church, concrete and frustrating, that can be effective.