Website personalization is an area I believe is significantly underused on dealer websites.
Firstly, I agree with Joe's point that your number 1 design consideration in implementing any personalization in an automotive website (or indeed any ecommerce site), is to understand how it will benefit your online visitors.
I think at the root of a lot of the criticism personalization receives is because of the complex way it's been implemented. If it's trying to do something inherently complex like predicting vehicles/products that a customer might be interested in, then the risk of this backfiring is going to increase. We understand what the input variables are (the current shopper's actions and other shopper's actions) and what the output is (a list of suggested vehicles) but we've no insight into the "algorithm black box" that comes up with this list, and this makes us suspicious.
However,
personalization does not need to involve a complex algorithm. There are several "not so big data" ways it can be used to good effect and at lower cost and risk. For example, if a user has arrived from an Adwords campaign "cheap cars in <your area>", then it's a good bet that the shopper is budget constrained and your website can then highlight cheaper inventory to them and emphasize your finance offers. I wrote an
article on my blog a few months back with a list of personalization ideas for dealer sites.
As with most website enhancements, implementing personalization should be an iterative process rather than set and forget. The feature should be tracked with your analytics tool of choice and different variations of it could be A/B tested to see which gives the best results.