On 6 September 2007, one day after unveiling their new Catalyst/fglrx Linux driver, is when AMD lifted my embargo that allowed me to exclusively explain their open-source strategy in detail.
The first documentation and driver code (for RadeonHD) didn't come that day as the Novell/SUSE developers were still under NDA at the time and busy churning out code, but Egbert Eich, Luc Verhaegen, Stefan Dirsch, and Matthias Hopf (the original xf86-video-radeonhd developers) ended up celebrating on this day from Nürnberg anyhow once the article was published.
It was then on 17 September 2007 is when the RadeonHD open-source driver was released.
For some reference to how this AMD open-source strategy began, read This Is What Started AMD's Open-Source Strategy -- the letter that I made public last year that revealed the early details when the aforementioned SUSE developers volleyed a letter to AMD about doing an open-source driver with open documentation.
AMD still not have the best open-source support available with it still taking months for new hardware enablement for major product launches (i.e. the still-lacking Radeon HD 7000 series), power management still leaves a lot to be desired, the overall performance isn't good, there is still no UVD video support, some features are still lacking (e.g. CrossFire), and not all are satisfied with the amount of documentation that AMD has ultimately released. However, with an open-source AMD we're certainly much better off now than we were five years ago.
As usual with celebrating this anniversary, the celebrating will continue in two weeks time from XDC2012 Nürnberg. Prost!