It's not an official video showing off weapon customization, but it's someone playing the latest alpha build, and showing off the weapon customization. It's a decent demonstration, the video also demonstrates weapon recoils and many more.
The customization seems a little bit deeper compared to Bad Company 2 since weapon attachments are now seperate. This is the latest alpha build of the game, and already you can tell it still needs further testing, a lot of bugs are shown in these two videos.
There's a lot of work to be done, but they still have a few months to get Battlefield 3 ready for release. Battlefield 3 will be out on October 25 for PC, Playstation 3 and Xbox 360.