With Linux we can easily clone an installation, or move hard drive between different systems. The hardware changes normally don't make much of a difference. BUT, with modern Ubuntu systems - and other distro's I'm sure - the network card can cause a problem. This comes up with virtual machines (with VMWare, Xen, KVM, etc.) when a copy of an existing guest install is used to create a new virtual machine.
The results of these changes normally show up as an error something like this:
SIOCSIFADDR: No such device eth0