It looks like Sony leads the race to get BSI sensors into production. Just announced Sony 2009 camcorder lineup features Back-illuminated Exmor-R sensor. Sonystyle also has a video on the new sensors.
Sony says that its BSI sensor provides approximately 2x increase in sensitivity compared with conventional models. However, InfoSync observed just 50% improvement in brightness and exposure comparing BSI-based HDR-XR520V with conventional HDR-SR12.
It's hard to say what is the pixel size in the new sensor. HDR-XR520V camcorder featuring 1/3.15" Exmor-R sensor has 12.1MP stills resolution, which corresponds to 1.1um pixels, if no tricks are used. Most probably, Sony interpolates the its 45-deg angled ClearVid sensor by a factor of 2, meaning that the physical pixel size is close to 1.6-1.7um or so.
The HDR-XR520V and HDR-XR500V camcorders with BSI sensor will begin shipping in March 2009.
Update: Camcorderinfo.com reports that the actual pixel count of HDR-XR520V sensor is 6.6MP, which means that my pixel size estimations of 1.6-1.7um are correct.