VirtualBox 2.1 was released a few days ago. One of the features that improved a lot has been Networking - setting and actual performance.
Previous to 2.1 release, simplest way to setup networking was to go with default setting of NAT. Though it worked, it had its own problems, For example Ping never worked, performance suffered since every packet had to be NATed. HostInterfacing was way complicated on all the plateforms except for Solaris.
The simplicity of setting Host Interface is now available on all the platforms (not just Solaris). Host interface uses the network connection of the HOST machine with out overheads.
To set it up, launch VirtualBox 2.1.
Click on "Settings" as shown below:
It pops up the following window where select "Network"

Select Adapter Type to be either PCnet Fast II or III if you do not know the one available on your machine.
Select Attached To Host Interface ==> to make use of Host machines interface
And select an Host Interface from the list of Host Interfaces available.
That's it. You are done and you will have a very good network performance







But this time, I wasn't scared at all, as I knew that it is an expected problem with Ubuntu - everytime, Ubuntu is patched/upgraded, it is expected to run into this problem.