The short version: old school class names changed to namespace versions. Read our previous notes before upgrading!
Today VHS 2.0 was released to TER. Before you upgrade you should read our previous notes about the changes: http://fluidtypo3.org/blog/news/coming-soon-vhs-20.html.
The most important thing to notice is that we have switched to namespaces. VHS now uses the FluidTYPO3\Vhs namespace which means you should change all your Fluid namespace inclusions. As the previous entry says we've also had to rename a few sub-scopes to avoid reserved keywords - so beware that you may have to update your templates not just regarding namespaces but depending on which ViewHelpers you used, also several ViewHelper tags. This is the main reason that VHS now has a new major version number.
VHS 2.0 will be a pre-requisite for using the new FluidcontentCore extension that is also coming up.
The FluidTYPO3 team