Oracle just released VirtualBox 4.0 couple of days ago.
I always prefer Sun VirtualBox. Not only VirtualBox is free, as it is an Open Source Software and also, VirtualBox run better and faster on my Fedora 14 notebook, as compare to VMWare Workstation. My personal experience is that VirtualBox is lightweight and need lesser hardware demands as well as good for personal virtualization needs.
VirtualBox 4.0 has introduced lots of new features, you can read from the #Changelog at the official site.
Install VirtualBox 4 is very easy.
#yum localinstall VirtualBox-4.0-4.0.0_69151_fedora14-1.i686.rpm
I use yum localinstall instead of rpm -ivh, to resolves all the dependent packages automatically. Btw, you can simply execute yum install VirtualBox if you import virtualbox.repo file into the YUM’s /etc/yum.repos.d/ directory.