I use Deuces Cracked and I am extremely happy with them. An instructor will typically do an eight episode series with the first episode or two giving the theory and than moving on to hand histories (lots of hand histories with great in depth analysis) and then usually some live play videos where you can see the theory put into practice. Also there are forums and the coaches are very active there. You can watch the videos online or download them to your computer.
How effective are they? You get out of them what you put into them. If you watch them while drinking a beer and IM ing freinds not so much. If you take notes rewind to interesting spots and post questions for the coaches they are worth every penny. I credit DC and this site for turning me into a moderate winner at the micros. That may not sound like much but I was a losing player and now I am winning and getting better all of the time.
Having said all of that about working at the videos, I will admit that I am not above watching the occasional video about a game I don't normally play while having a bit of the "captain" in me while unwinding late at night but I'm weird like that.
One more thing to end this novel: I hope none of the great Drag the Bar coaches that post here are offended by my mentioning a different site. I have total respect for what you guys put out but I started with DC and I'm an old curmudgeon set in my ways.
Bill