We've all heard of "banner blindness" - the phenomenon of completely ignoring anything that resembles an ad when surfing the website.
Image Source: Jakob Nielsen
For this reason you want to avoid sticking important links and calls to action in the right hand sidebar. You especially want to avoid colors and fonts that resemble typical paid search ads.
Home page
Product page
Silkfair product page
Same goes for navigation menus:
There are instances where even Internet Retailer 500 retailers really display Adsense on product pages:
I strongly believe reputable retailers should completely avoid paid search ads on their sites. But what's worse, on Chapters Indigo, you can't even distinguish the ads from the recently viewed products from the cross-sells because they use the exact same colors and fonts.
Further Reading
Yes, there is solid research to back this argument up. Thank you, Mr. Jakob Nielsen:
Banner Blindness: Old and New Findings
Fancy Formatting, Fancy Words = Looks Like a Promotion = Ignored