I have nothing against Unity but on a least on one of my very old machines is runs too slow. There are too many delays as the machine tries to do something that should be routine. Running the Classic Gnome is quicker on that machine. I also found Classic Gnome snappier on my netbook (NC10). It was simple to do in the last release, just select Gnome as one of the options from the log in page.
So, I upgraded the netbook to 11.10 and it automatically reverted to Unity. Not a surprise, I thought. I went to the log in page and clicked on the gear wheel but there was no option to load in Gnome. It is no longer included in this latest Ubuntu release!
Adding Gnome is very simple and there are two options, the traditional Classic Gnome, or the latest Gnome Shell. Gnome Shell is great.
If you want Classic Gnome go here for excellent instructions.
I went for Gnome Shell on my NC10. All the advantages of Unity but with a look I prefer, quicker (I think) and icons that are a better size for the small netbook screen. If you want a very simply way to install Gnome Shell go here for excellent instructions. There is even a button there that you can click and the rest will happen automatically.