I'm sick of hearing about how to "monetize" forums. Stop it! You are all killing the market.
Stepping out of topic for a second--many of us run forums out of our own pockets, and depend on ads to help pay the hosting bills. I have always used ads, and our site members are understanding enough to not only tolerate what few ads we have, they also understand why we need them, and why (for affiliate sales, such as Amazon) their purchases or clicks help us out in some small way.
I do dislike sites that cram way too many ads on their pages, including forums, so I try to make my ad placements where they do not interfere with content. In a forum, I'm with those who feel that unregistered guests will get ads in places that registered members would not. I'm fine with that but again, it needs to be kept in check or you face driving visitors away.
In my case, "monetizing" only helps me pay the bills, so I'm putting out much less of my own money. The ultimate goal is to have the sites support themselves from affiliate sales and ad clicks. It's not greed, it's survival. Not all of us are in it for a monetary profit, but our own "profit" comes from running a self-supporting site that users can enjoy visiting. If that means my ads are in less than favorable positions, then so be it...I'll sacrifice some income to keep the clutter out of the way of our site content.
And yes, we need iTrader...
The large forum I run has a very active marketplace community, and if we had Sphinx support and iTrader up and rockin', I'd have the site owner sell of the vB license so we could hook into the goodness that is XenForo.
(My own xF license is for another site I'm building.)