Here's some recent changes in Amazon's associate agreement (for people who earn money off links pointing to Amazon's products).
Amazon's announcement of these changes focused on the benefit to associates who used a link to myhabitat.com, who have 30 days to earn rather than the usual 24 hours. They failed to highlight the change that stops you earning if a user who clicked your link follows any other link to Amazon, not just that of another associate. (Update (late June): This has now changed to "any Special Link", i.e. another referral.)
Is this reasonable? Arguable. I suspect they've run the numbers and found quite a few people look around before putting an item in their cart, and in that case you might well lose out on what would otherwise have been a valid sale.
They are also forcing all non-small-claims disputes to go through arbitration. Wonder which lawsuit that was inspired by.