The build was original targeted as Opera 7.6. But because of the numerous improvements, it has made itselfs to Opera 8.0. For detail of the various changes, see the changelog.
Among all the changes, the most impressive one is undoubtedly the voice technology (by IBM). Now user can use voice commands to control the browser; TTS by highlighting and pressing V; and interact with XHTML+Voice enhanced websites.
The TTS is quite good. It will pause a little bit before and after elements like strong, em and a, and words in full uppercase like ABC.
However, it seems that only English is supported. Also, when it comes to sentence with punctuation marks next to an element, the resulting speech can be very weird. For example,
Opera is cool. will be spoken out as
Opera's (pause) cool (pause) dot. So the current engine cannot handle paragraphs that are heavily hyperlinked well.
P.S. By the way, Opera 8.0 Beta 1 has a popup notifier like that of the Gmail Notifier. The only difference is that it is shown on the top of the screen, not on the bottom. Look weird to me.