I had network issues after upgrading to Ubuntu 11.10 which has the linux 3.0 kernel.
I used this guide to compile the r8168 driver however, I needed to alter the Makefile to support for linux 3.0 kernel.
#KEXT := $(shell echo $(KVER) | sed -ne 's/^2\.\..*/k/p')o KEXT := $(shell echo $(KVER) | sed -ne 's/^\.[1-9]\..*/k/p')o-
Now you should follow the rest of the guide.