This, for example: "We do, however find some price variations for Kindle ebooks on www.amazon.com, depending on if the user is logged in to the site or not." [http://arxiv.org/abs/1307.4531]
Also see Figure 1 for the evidence of prices highly varying over time. It implies that different users pay different prices within small periods of time.
One of the elements is that "the effect of such discrimination may be substantially to lessen competition or tend to create a monopoly in any line of commerce". I don't think Amazon's dynamic pricing satisfies that element.
That's up to government commissions to decide whether Amazon "tends to create a monopoly" with dynamic pricing. Amazon discloses nothing about its technologies to the public. What we see is, (1) Different prices for different users; (2) The conflict of interest with the merchants Amazon.com hosts, as Amazon serves both as a host and a reseller; (3) Amazon has an access to other merchants' traffic and prices, and is able to diminish their chances to compete with the service.
