Updated blog post: I just downloaded and installed Symbian Anna (firmware version v.022.014) on Nokia N8. The file was about a 22 MB download from the firmware over the air (FOTA) selection in Settings -> Phone -> Phone management -> Software updates menu.
It’s also available for Nokia E7, and probably C6 too (I could not confirm yet). Edit: Press release from Nokia confirms it should become available for all the Symbian 3 devices. There are release notes with new features and fixes on Nokia Conversations blog.
The first new thing you will notice are the new icons and the portrait mode virtual QWERTY.keyboard. Application icons are updated too.
I will write about my experiences, when I played with this for a while. After the first two hours, everything seems to work fine.