|Ahhh... the Unity! :)|
Although the better GPU, CPU and RAM... you have, will always be welcomed but yet if all you want is to run Ubuntu as fast as you can without a lot of fancy effects then as with the 10.10 version, below hardware requirements should be more than enough.
*. Processor - 1GHZ (for an i386) is recommended for the Desktop installation.
*. RAM - 512MB, although you could still run it smoothly with a slightly lower RAM, in my experience anyway.
*. 5 GB HDD space - This however may change depending on the applications or the amount of packages, still there won't be huge difference.
*. Resolution - 1024 x 768 is enough. If you have a touch sensitive screen, then you'll love some of the things that Unity is capable of!.
Anyway, this is something that I really like about Linux in general, unlike with Microsoft, they don't forcefully or unnecessarily to be precise, put a lot of "requirements" thus making the users to buy a whole new PC rather than using the "fully working" PC they currently own, LOL.