It doesn't require a lot of time to share the fair amount of information I collected while writing Hardcore Erlang and the feedback makes it worthwhile, even if the money isn't.
There's a marketing sideline to this as well. A member-only mailing list is a great way to size up the market. Perhaps there's none, perhaps there's a sizable one. If I get swamped with subscriptions then I could invite other experts to help me and, perhaps, sell products or services my subscribers would be interested in.
Also, I have a number of crazy Erlang projects in mind like a Mac Cocoa bridge, trading software and others. I could dedicate myself full-time to writing code for The Erlang Journal, if the number of subscribers allows it.
In the meantime, I don't look to solve all the problems that folks bring up, I just have to solve enough problems for them to keep coming back.
There's also a public source code repo at http://github.com/wagerlabs/thinkerlang/tree/master that you may want to take a look at.