Graph look like this : http://twitpic.com/7l215z/full
OS : Ubuntu 11.10
GNOME Shell 3.2.1
that is actually correct, however it does draw the pie ring to big when only one drive is available.
On this picture it looks like that the graph represent the CPU / Mem / swap and not just the disk usage.
I think it's more usefull than the disk usage. Is there any way ti get it work that way ? (an option or a fork ? )
Ahh. Now that gheaeckkseqrz explained it more clearly, I gotta say, I've wondered the same thing.