Alan Taylor and Anil Dash report that Amazon is rolling out tags in a big way. In a discussion board message, Amazonian Blake Scholl announced that 50% of Amazon customers will see the tagging features at this time.
You will be able to apply tags to any item on the Amazon website and your tags will be collected under your profile. I like Alan's term for that - a taglist, like a wishlist. I can envisage Amazon adding RSS feeds later, so you can subscribe to tags and your friends' tags. For now Amazon has the whole "customers who used this tag also used..." thing going on, as a tie-in with their existing personalization features.