Re: Restoring Ubuntu
You can do that (untar an entire OS onto another computer), but that doesn't mean that it's going to work correctly, or at all. If the hardware is identical in every respect (which it won't be -- the partition UUID for example is always different), then it could theoretically work, if you installed your Grub boot system the same.
It sounds like you are looking for something like clonezilla. If you use clonezilla to make an image of a hard drive partition, and then you restore that image to an equal or larger sized partition on another computer, you will have a bit-for-bit true copy of the original. Then you only need to work out the adjustments for any hardware differences, such as UUID numbers, and you will have the same software on a different hard drive.
Intel Core i7-950 / Asus P6X58D-E / Nvidia GTX480 / siduction 64-bit on OCZ Revodrive SSD / KDE4.10.2/ Kubuntu 13.04