A lot of websites either break or they intentionally disable some specific functionality if you have adblock enabled. For example, you can't submit reviews to williams sonoma unless you disable adblock. Maybe because there is a third party handling the reviews.
Frequently I have to add these websites to adblock's whitelist to do one specific task. Of course I forget to ever take them off the whitelist, and then next time I visit I wonder why there are ads.
Suggestion: allow the user to set a whitelist expiration of 1 hours, 24 hours, etc. for a specific website. This way there is no need to remember to take a website off the whitelist.