I subscribed to Dave's School of Podcasting after listening to several episodes of his show. There are other people out there who teach podcasting with a bit more hype, pomp and circumstance, but I don't believe that those methods will produce long term results.
What I like about Dave is he seems to actually care not only about people individually, but about the podcasting field in general.
Dave will never tell you to exchange reviews. I know this practice exists, and yes, of course I've been tempted to go this route myself, but think about it.... why should you get someone to review your show who will never listen to it? Don't you want REAL listeners to review your show?
You will only gain listeners by producing great content and marketing your show to actual potential listeners.
Also don't be fooled by Dave's humility. He really knows his stuff and if you spend a few shows listening to him, you'll start to learn it too. I've greatly improved my podcasting skills by listening to his show, and being a member of his School of Podcasting hasn't hurt either because he always answers my questions, usually within an hour of my emailing him. If you are going to pay for a podcasting coach, the value you get from the School of Podcasting can't be beat.