I am also running Ubuntu 10.10 64bit. I installed both Arduino IDE version 018 and 021.
I had the same error "programmer is not responding" with my new Arduino Uno but it is solved for me now.
This is what I did:
Installed 018 from Ubuntu universe repositories via the software center under applications. Just search for Arduino and it will pop up in the list and click install.
I downloaded the 021 version from the Arduino website. (the tgz file for linux/ubuntu). I unpacked this to my home dir in /home/ruud/Coding/Arduino/arduino-0021/ and added a custom launcher to the panel with these properties:
Type: application
Name: Arduino IDE 021
Command: /home/ruud/Coding/Arduino/arduino-0021/arduino
018 does not seem to work. What I did was follow the instructions here:
http://www.ladyada.net/learn/arduino/lesson0-lin.html
to uninstall brltty
Next I started the Arduino IDE 021. I selected the UNO in the Tools > Board list and I changed the serial port to /dev/ttyACM0.
Next I could happily upload my sketches again to Uno and they run properly now. I am not sure which step in this did the actual work but by following my journey, you should get the same result I hope.
Good luck!