Article 66 of this set of directives, http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:337:0011:0036:En:PDF, from the Official Journal of the European Union states that:
“Third parties may wish to store information on the equipment of a user, or gain access to information already stored, for a number of purposes, ranging from the legitimate (such as certain types of cookies) to those involving unwarranted intrusion into the private sphere (such as spyware or viruses). It is therefore of paramount importance that users be provided with clear and comprehensive information when engaging in any activity which could result in such storage or gaining of access. The methods of providing information and offering the right to refuse should be as user-friendly as possible. Exceptions to the obligation to provide information and offer the right to refuse should be limited to those situations where the technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user. Where it is technically possible and effective, in accordance with the relevant provisions of Directive 95/46/EC, the user’s consent to processing may be expressed by using the appropriate settings of a browser or other application. The enforcement of these requirements should be made more effective by way of enhanced powers granted to the relevant national authorities.”
It’s not clear to me what “third parties” constitutes, but I assume it does not include the owner of the website the user is visiting. So Google Analytics / Ominiture Site Catalyst would count as a third party.
It’s possible you could interpret the use of an eCommerce site as a user explicitly requesting the service of browsing products for the purpose of purchasing. If you could, then the storage of analytics tags could be interpreted as being necessary to provide an effective browse and purchase experience through process of analysis and improvement. Then it might pass as being the “legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user”. It does feel rather tenuous though.
This is all personal opinion and is not legal advice. Please seek somewhere else to pin the blame if you get taken to court for not asking your customers for permission to store cookies!