Accessing an Ubuntu desktop from Mac OS X Lion [UPDATED]

I've got this working now, but it's more complicated than it ought to be...

My home machine is an Apple iMac running OS X Lion.   The screen is very big and clear, so I'd like to use the Mac screen for everything when I'm working from home.

My company machine is a laptop running Ubuntu 10.04 LTS.    I'd like to access the laptop screen remotely from the Mac over my LAN, so that I don't need to use the laptop screen and keyboard when I'm working from home.

Surely with VNC, this should be easy... Just share the Ubuntu screen with VNC, and connect to it from the Mac.

• On Ubuntu: start the 'built-in VNC server (System / Preferences / Remote Desktop).
• On the Mac (Finder / Connect to Server / vnc://hostname)

Problem 1: The Ubuntu screen appears on the Mac, but updates are not shown.

• Cause: "xdamage" doesn't work.  This is a server-side optimization.  Apparently it clashes with something in the NVidia driver.  
• Solution: A workaround is to turn Compiz screen effects off on the Linux end: (System / Preferences / Appearance / Visual Effects).

 Problem 2: It's very slow.

• I've tried various VNC servers and clients to no effect.  It always seems unacceptably slow (and that's on a quiet wireless LAN between two fast machines).
• One solution is to use FreeNX server on the Ubuntu box, and the NX4 Beta Mac client from nomachine.com.   That works nice and quickly, but it doesn't re-publish your existing X desktop.  Instead, it creates a new desktop instance and serves that.  It all seems over-complicated, so I'm going to give up for the time being.
• I'm told that Nested-X is probably the way to go - but I'm guessing that would be a pain to configure.