Under Windows a simple Addon exists with wich I can sync my funambol events and contacts with Thunderbird and Lightning. I couldn't find such a tool for Ubuntu yet but it would be very helpful for me.
AFAIK, there are only "inofficial" builds of the Funambol add-on for thunderbird. Take a look at memotoo.com's site, there are build for Windows, Linux 32/64 bit and even OS/X. The site is in german, but you can set the language to english using the controls at the very top of the page.
At the first page, look for the buttons to select your application (you may have to scroll until you get the thunderbird icon):
Click on thunderbird icon to get the download links displayed:
Now, just download the add-on that matches your thunderbird and ubuntu version (32/64 bit). There's even a short documentation how to install the add-on (of course, you'll have to adapt the url to point to your funambol provider).
I'm using those add-ons with lucid, oneiric and with Win7 - works like a charm!