You can find more info about product at:
http://www.psoft.net/promo/

And the new features at:
http://www.psoft.net/HSdocumentation/new_features.html

Some key features:
New end-user user interface
IMP WebMail
Urchin support
Improved Private Label Reseller support
SignupGuard fraud protection for automatic sign-ups
Ability to move accounts between resellers.
Major billing improvements.
SiteStudio 1.54 included.