I don't think Fork CMS is very well known outside Belgium (it is being developed by a Belgian webdevelopment agency, Netlash), but it's actually starting to get more popular here. We're seeing several new deployments of Fork CMS "in the wild".
That's what prompted me to make a Varnish "template" to handle the caching of a Fork CMS. I've pushed the code to my github repository, Varnish 3.0 Configuration Templates.
For now, since a PHP Session ID is generated at every page request, I'm making all pages "static" except the /private and /backend pages that require a login. If you've got any recommendations, I'll gladly hear of them!