Here's my first go with the VirtualBox. (For a detailed review I found Jason Perlow's article very useful
Virtualization smackdown: Sun xVM VirtualBox 1.6 vs. VMWare Server 2.0 Beta 2)
I had been enjoying a fedora laptop. (Yes, its not Ubuntu. I will write in another blog about my reason for dislikeness)
Then I gave a shot to redmond os in my virtual space. Both VMware and Vbox went smooth and great.
Here are the screen shots:
Fig: VirtualBox's "seamless mode" is the feature I love. Here is a screen shot with it. Notice the windows taskbar aligned with top and kde's taskbar aligned with bottom.
The desktop background is the default fedora's and then IE window running in the foreground.
In the last screen shot if you look closely, an IE window (right) is running in the guest OS and the Firefox window (left) is running in the host OS. Thats the beauty of the Seamless mode.Although VMware has been the industry leader and default choice for personal and enterprise level virtualization requirements for many years. But now Vbox is equally solid, feature rich and no less.
In short, I personally feel that over the time VirtualBox will carve a broader market share in virtualization. It has more support of host systems.
Where VMware may become verticle solution for specialized needs focusing on datacenters with machines running on Windows/Linux hosts.