Inline advertising is a potential boon for web apps to make more money, but it's fraught with danger and bad kharma.

I think it could be done well, or something like it but you can't just plug it in.

And what about user generated content? Can I turn your words into ads? I don't think so!! 

More info;

http://searchviews.com/archives/2005/08/the_four_types.php

http://www.mikemoran.com/biznology/archives/2007/02/are_you_ready_f.html

http://www.vibrantmedia.com/