While most websites will be able to comply with a few simple tweaks to their code and the application of Cookie Control, some third party apps will be badly affected.
Google Analytics is estimated to run on 90% of websites. As an entirely cookie-based analytics solution it is not compliant with the legislation without the provision of explicit consent by website users. When the ICO tested this on their own site, only 10% of users actually opted into the service.
Obviously, an analytics package that only tracks 10% of users is hardly of use at all. Google's silence on this problem has been deafening. We can speculate that they're hoping the ICO will approve a global opt-in that will be valid across all Google services, or that an exemption will be made in the case of analytics. But in the absence of any solution from Google, webmasters may have to find an
alternative analytics solution that doesn't depend on cookies.
Websites dependent on sales from advertising will be harder hit. At the moment scripts from some ad networks deposit cookies in order to personalise ads on websites that users visit later. It's difficult to see how this functionality will survive when explicit consent is required in order to make it work.