CACert is utilized and deployed by OpenMoko on multiple systems.
On our Infrastructure we deploy CAcert Certificates on all SSL services.
Many systems have a x509 certificate signed by the CAcert class 3 Root Certificate http://www.cacert.org/index.php?id=3
To make full use of CA Cert your client software has to now about the Root Certificate. If this certs are not in place, depending on the client you use there will be a popup telling you about security concerns or in worst case it will fail entirely.
Integrating the Root Certs to your Application is the best way to archive more reliable encryption.
Applications where you might want to import the root certificates are: