Very good question.
Once I have struggled with myself.
See
Ireland Photos / Desktop Backgrounds / Irish Wallpaper for another example of a site that perhaps has a few too many adverts (but does bring in some half decent advertising revenue).
(I will be taking the annoying top right advert off completely soon as it doesn't earn enough to warrant its 'annoyingness').
I personally dont think you have too many adverts on your own site. but if it was me, I would mix the adverts in with the content a bit more rather than have them in separate columns..