For those who love linux but sometimes encounter themselves with an error trying to activate bridge networking in VirtualBox I want to give you what I found with 3.x version.
If you install the .deb package or install it from the repository it's probable that after you configure, let's say eth0 as the bridge interface you get an error: something like VERR_SUPDRV_COMPONENT_NOT_FOUND.
Basically the error indicates that the module in charge to bridge networking is not loaded, so if you "google" for the solution most of the results will indicate you to execute "/etc/init.d/vboxsrv setup". The problem with this command is not available in the installer package, to get it you must compile the source code but... :)
I found a blog written by Jeremy Visser where he indicates that the problem has a very simple solution: to load up the module which is vboxnetftl so to try you must type (as sudo):
If this works for you, just add vboxnetftl to /etc/modules
I hope this can help some of you. ;)