I had troubles with the Ubuntu r8169 driver and my Realtek RTL8111/8168B PCI Express Gigabit Ethernet controller for a long time.
Finally it semms that I found a solution for a stable ethernet connections: The new r8168 driver (Version 8.031.00 - found here on Google Code) seems to work quite good out of the box.
Just extract it, and run (as root) autorun.sh via
Of course, you have to do this after a kernel update once again.
Don't forget this - It frakked me one time!
Thats all 🙂
Seems to do it's work quite good