Check out eried's Arduino IDE Enhanced:http://arduino.cc/forum/index.php/topic,118440.0.html
The Leonardo is very fussy doing both USB comms and running sketches. I found if I hook up the USB directly to the "root hub" on my notebooks running XP, it tends to hang on uploads. I put it on a "USB Hub" and it fixed that problem. The problem I was unable to fix was the communications running a sketch and output to the serial monitor does not work on my XP machines but works fine on my Vista machine.
Anyhow, it's a good device but the guru's need to work out the kinks. Uno has had a lot of refining to get where it is.