We've had some advertising on this board before, and Seth canvassed our feelings about it before introducing it previously. Somebody or something has to cover the costs of the "free" Internet. This board is free for our use, and the breadth of discussion here also extends beyond what could be considered merely promotive of the Shangri-La Diet. If Seth wishes to recover his webhosting costs of running this board by allowing limited advertising, then that's his prerogative.
Lots of discussion boards have advertising -- some with more than what we've seen here, and often with ads between posts in a thread, where they're much more intrusive. As for the content of the ads, it's probably selected automatically by context-scanning for keywords of interest. This can result in some quite perverse selections for what is to be displayed, such as (for instance) ads for meat products being displayed on a vegetarian discussion board, where the context scanning picks up on "meat" where posters might be talking about how disgusting they find the idea of eating meat.