A recent question around the area of personalisation and customisation as part of the web offering of mature retail brands got me thinking about this post, because it's an issue I've seen with a number of organisations.
The first problem lies with semantics - i.e. the definition of personalisation vs customisation with respect to the use and design of websites. I see one as automatic audience targeting and the other as the ability for the customer to manipulate the website to fit their needs... the former as personalisation and the latter as customisation.
As a business your first priority is to define your understanding of what each one means so that all parties are working from the same standpoint.
In terms of personalisation as per the above definition then, I reckon this is the future of customer focused business intelligence. It is about understanding the customer, either as part of a larger group or as an individual and then presenting them with their own unique customer experience. User Experience experts can help with audience segmentation analysis, identifying key audience groups and defining an experience that best fits/targets them. Similar to personas, but a bit more generic and more automated; with some business logic that leverages the user's profile data and preference information along with their browsing habits to present them with the scenario that fits them. From a technology and business intelligence perspective you could implement real time tracking and analysis of user behaviour, underpinning the automated tailoring of content presented as the user progresses through their experience. Sort of an extension of what I was talking about in an earlier post on the targeted channel experience.
In terms of customisation, from an online retailing perspective, I don't really see the benefits against cost of development. You could provide a 'Windows Live' type page where users can customise what they see and how they see it, but frankly with mature retailers I don't see who would really use it. Shared personal profiles that users can customise similarly don't really make sense for this type of business, or at least not until social networking in the mature brand shopping context becomes significantly more embedded, if it ever does.
However, simpler customisation linked to personalisation, could be very useful; for e.g. possibly like a variation on the Amazon recommendations model, where the user could be presented with an option alongside product displays allowing them to select items into a 'not interested' and 'I like' category that can then not only automatically build them their own page they can refer to and edit later, but also feeds into the intelligent browsing stuff I was talking about in the previous paragraph - i.e. this information is used to understand what the user is looking for and preferentially feed them those products as they browse or search, thus enhancing the targeted browsing experience.
This could help retailers improve their offering to customers online, increasing not just browse to sale conversions, but also brand loyalty because the customer feels understood.