Can the new Sony tablet be used as a wireless or tethered viewfinder for the A900, does anyone know?

I'm fairly sure not. You need an HDMI connection for reviewing images only and no live viewfinder feed is possible from the A900 - at all.

David

and the S tablet, beautiful btw, does not have an HDMI port -but support USB host.

Thank you for the response, I had hoped it may be used in a way similar to the Apple iphone, i.e., as some photographers in the US have reported doing.
I have just visited the Luminous Landscape website where Michael Reichmann has just reviewed the Sony Tablet S. It's covered in the "what's new" section, and he has answered all the queries I had re the Tablet.

The iPhone can only function as a remote release - there is a tethered mode available for the a900 on, for example, Mac or PC laptops. But this only allows a limited range of control via USB, and review of the image/histo etc, and remote saving of the image. This type of function has existed from the very beginning of Minolta digitals (initially as 'Dimage Transfer') and with the Konica Minolta A2/200 allowed live viewing and shooting on a PC - years ahead of its time.

As far as I know there's no true wireless remote viewing/shooting for any current Sony Alpha, though some kind of HDMI/USB rig might be possible with the new models.

I can shoot on my Alphas using the EyeFi X2 Pro card and save to an iPad/tablet/laptop directly, but not see anything except the images arriving - and no control from the tablet device.

David