I have a Windows XP host machine with guest Ubuntu OS. I started with the latest VMWare player and benefits I noticed:
1. Hassle-free installation of Ubuntu
2. Seamless integration between guest and host
o) You can copy-paste files across host and guest!
o) Clipboard is shared bi-directionally
3. Very good performance: applications, network, and devices (DVD)
4. Display scales well on bigger screen with VMWare tools.
5. Alas! you can have at-max one processor simulated
1. Easy Ubuntu installation
2. Most horrible and pathetic clipboard sharing. Contrary to claimed, it provided one-way clipboard from guest to host.
3. XP clipboard stopped working and never worked till I stopped VirtualBox.
4. Supports VMDK files but it's crappy, buggy and leaves VMDK in an un-usable state. I could never run my VMDK with VMWare later.
5. Can simulate up to 4 cores.
6. Supports shared folder between host and guest. I think it's a generation behind what VMWare provides.
7. Very slow performance: application, system start-up/ shutdown or stand-by. This is the biggest letdown.
My verdict: VirtualBox has miles to go and I am using VMWare still :)