The Softimage 2010 version is finally out. You can download the demo on the Autodesk web site.
I was happy to see that it comes with Mental Ray version 3.7.55 ... Maya uses version 3.7.53.
It is nice that both software are finally using the same version. Softimage was always one Mental Ray version behind.
But at first glance there doesn't seem to be a whole lot of 3.7.5 features implemented in Softimage 2010. I will investigate more. The nicest feature I can think that would be usefull is the map data which can be used to save particle information. This could prove useful to pass particles system from Maya to Softimage. I will definitely look into that.