Sony announced a four-colour sensor with two different kinds of green, one of them called 'emerald' (a blueish green), as early as July 2003---see
http://www.imaging-resource.com/NEWS/1058329666.html. I think the first Sony camera featuring this RGBE sensor was the Sony Cybershot DSC-F828, released in November 2003. The current Sony Alpha DSLR cameras still seem to have Bayer filter arrays with two different greens, even though they don't make a fuss about it in the tech specs or in the advertising materials. I guess the difference between the two greens today is far less than it used to be in the F828's RGBE sensor ... umm, does anyone know for sure?
Anyway---when converting a current Sony ARW file twice, once with ACR 5.4 (or earlier) and once with ACR 5.5 beta, then the difference between the two results will be so tiny it's virtually invisible at 100 % view. Basically, ACR 5.5 will yield slightly better tonal separation and colour separation, at the expense of slightly less acutance (lower micro contrast). The most significant differences between the two conversions will occur around high-contrast edges. However, in order to notice you'd have to compare at 400 % view or so.
-- Olaf