Sitefinity 4.0 is planned for official release in early 2011.
The current CTP is not intended for production web sites. It is only intended for local testing and is not yet feature complete. We're using it to gather early feedback about the product.
Is your project targeted for this year? If so, I would not recommend using early builds of 4.0. If the projected is targeted towards mid 2011, then it might be a good fit.
Telerik | Sitefinity CMS