Kyo, if you provide code for the tall banner, I'd be more than happy to place it on my site. Also, why not provide a sidebar beside the comments, just below the one-column comics with the PW code by default (authors have to activate the ad option, right?) :-)
For what it's worth when I've bought ads on PW I have gone for leader board/banner ads located at/near the top of the page where folks will see it coming onto the site and only done skyscrapers/boxes on things where the content extended downwards to the point folks would reasonably be expected to see it in normal viewing of the content. Buttons or anything else that is hidden down below blogs & comments etc. that most folks would never see on a usual visit I tended to ignore unless the bidding was @ $0.00 on American traffic, of course that position was the reason the bidding was bunk I think.
I know this is not exactly what's being discussed here... but apart from voluntary ads supporting CF... can I include ads in my webcomic pages where the revenue goes to me? To support my work? Just asking. :)