To make it work I had to create my own sparse bundle with a plist file in it to associate my MacBook’s unique id with the time machine image. Leopard and earlier releases of OS X would create a sparse disk image with the name from the network cards mac address, but in Snow Leopard it uses the computer Hardware UUID. I imagine this is because notebooks can have more than one mac address, one for wired and one for wireless.

How to create a sparse bundle in Snow Leopard

Step 1: Create the disk image with your computer’s name:

hdiutil create -size 500G -fs HFS+J -volname 'Time Machine Backup' -type SPARSEBUNDLE computer_name.sparsebundle

Step 2: Create a file called com.apple.TimeMachine.MachineID.plist inside the sparsebundle folder and fill it with the following:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.backupd.HostUUID</key>
    <string>UUID_STRING</string>
</dict>
</plist>

Make sure you replace UUID_STRING with your unique machine identifier. This can be found by loading System Profiler (Hardware UUID).

Step 3: Transfer the sparse bundle disk image to your Ubuntu computer:

rsync -avP computer_name.sparsebundle username@ubuntumachine:~/