Amazon.com has begun the transition away from tabs as a navigation interface. They're probably testing it on some subset of sessions, and I'm actually still not seeing the tabs when signed in, but if they've gone so far as to create an entire page explaining the new navigation then I don't see them changing back.
It's not as large a leap as it once was. Amazon has been down to 3 tabs for a long time now. The first iteration of Amazon was text only. When the music store came along, tabs were added along the top, a green tab for books, a red tab for music. Then came the DVD and Video (VHS) stores, combined in one purple tab. And tabs continued to be added to the right as stores were added. Here's a snapshot from the Internet Wayback Machine from October 1999. Most retail sites with a similar variety of product selection copied the leader and put tabs across the top.
At some point, there were too many stores and not enough room for tabs along the top. Some designer mocked up an Amazon homepage with three rows of tabs as a joke; I probably have a copy of that somewhere in my old work e-mail archives. It looked like the bottom half of some toothy monsters mouth, or a crowded graveyard of retail tombstones. This led, eventually, to a design that aggregated all stores under a single tab that would fly out a list of store links inline.
Even when it was just a bookstore, Amazon's customers started their interactions with the site through search more than any other site feature. It makes sense when the catalog of books is some 2.5 million items long. Now that they've got who knows how many items in their catalog, search must account for some 60% to 70% of how customers dive into the store.
Mostly, though, the end of the tab navigation signals, for me, the passage of time, not just in my life, but on the web.