My install did not set the user groups correctly. From a shell, enter 'groups' and see what user groups you have assigned. dialout and uucp are the main groups that affect the connection.
Now that you have all the "goodies" from the Ubuntu repository, you might want to try downloading IDE v1.0 from the Arduino site now. Unpack it into a local directory, then run the arduino shell script in that directory. That should run v1.0. If you run the Ubuntu-installed version from an icon, you get v0022.
See if you can run that version without requiring root login.
edit: This bug will also affect the ethernet code in both versions.
http://code.google.com/p/arduino/issues/detail?id=605
You might want to apply that fix if the ethernet interface crashes.