After installing Arduino 1.0.1 (from the source on arduino.cc) I get these errors running the IDE:

Experimental: JNI_OnLoad called.
Stable Library
=========================================
Native lib Version = RXTX-2.1-7
Java lib Version = RXTX-2.1-7
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL
check_group_uucp(): error testing lock file creation Error details:Permission deniedcheck_lock_status: No permission to create lock file.
please see: How can I use Lock Files with rxtx? in INSTALL

The fix is simple, but hard to find. As root, add your user to the "lock" group (either edit /etc/group, or usermod -G gill,lp,wheel,dialout,lock gill)
Then change the permissions and ownership on /run/lock directory: chgrp lock /run/lock ; chmod g+rw /run/lock
There is also some problem with Arduino Leonardo getting captured by the modem manager. I found a solution in the Arduino forums. "modem-man" attaches to the tty. If you run "sudo lsof /dev/ttyACM0" right after you plug in the Arduino Leonardo you can see it.

systemctl stop NetworkManager.service

and

sudo killall -TERM modem-manager

To fix this permanently, you can edit /etc/udev/rules.d/77-mm-usb-device-blacklist.rules and add:

# Arduino
ATTR{idVendor}=="2341", ENV{ID_MM_DEVICE_IGNORE}="1"

No