You may have read in one of my previous postings about Ubuntu 11.10, that nautilus-gksu (Open as administrator) seems to be broken in Oneiric, even when it displays in Synaptic as installed.
It seems that nobody has got around to rebuilding the nautilus-gksu extension for Nautilus 3.x
The good news is that it does get installed to /usr/lib/nautilus/extensions-2.0/libnautilus-gksu.so
But Nautilus 3 ignores it, so you need to copy it to /usr/lib/nautilus/extensions-3.0 directory …
First make sure nautilus-gksu is installed:
sudo apt-get install nautilus-gksu
Then copy the libnautilus-gksu.so file to /usr/lib/nautilus/extensions-3.0 :
sudo cp -v /usr/lib/nautilus/extensions-2.0/libnautilus-gksu.so /usr/lib/nautilus/extensions-3.0/libnautilus-gksu.so
Now restart Nautilus:
nautilus -q
Or log off and on again.
You should now have an option to “Open as administrator” in the Nautilus right-click menu 
This is an “at your own risk” workaround, but I’ve been using it for a while now and haven’t seen any issues.
I’ve now sorted nearly all the gripes I had with 11.10
