I'm in a similar situation. I have an affiliate site (posters) in particular that gets a decent number pageviews a day, and it does make some money, but I'm very uncertain about putting adsense on it. I'll lose some visitors and hence some sales, but then, most visitors don't buy anything anyway, so why not.
Maybe I should put adsense adds on the site. I only make a handful of cents from the average visitor, so it might make more with ads.
My affiliate commissions are down a bit but it's been more than made up for by Adsense.
I also think that my sales would have been down regardless this past month. My own Adwords campaigns were not running for about three weeks of the month due to a lost debit card and the bank taking forever to get me a new one.
I put up adsense skyscrapers on my site where I sell a little piece of my own software (no affiliate thing). The banner is filled with ads from my direct competitors selling similar programs and people love to click on them but my own sales did not drop. Perhaps potential customers think that I must be very confident of my product :)
Under the line Adsense raised the sites revenue by about 7-10%.