I am having the same problem yet this is with a newly purchased board, and with IDE version 1.5.6-rc2 (latest one downloaded). Sometimes when I open the Serial Monitor and quickly there-after try to upload it works, but it's very iffy.
Here's a copy of exactly what I'm getting:
Sketch uses 18,138 bytes (63%) of program storage space. Maximum is 28,672 bytes.
Global variables use 520 bytes (20%) of dynamic memory, leaving 2,040 bytes for local variables. Maximum is 2,560 bytes.
Forcing reset using 1200bps open/close on port /dev/tty.usbmodem1421
PORTS {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.Bluetooth-Modem, /dev/cu.SarelsiPhone4S-Wireless, /dev/cu.usbmodem1421, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.Bluetooth-Modem, /dev/tty.SarelsiPhone4S-Wireless, /dev/tty.usbmodem1421, } / {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.Bluetooth-Modem, /dev/cu.SarelsiPhone4S-Wireless, /dev/cu.usbmodem1421, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.Bluetooth-Modem, /dev/tty.SarelsiPhone4S-Wireless, /dev/tty.usbmodem1421, } => {}
PORTS {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.Bluetooth-Modem, /dev/cu.SarelsiPhone4S-Wireless, /dev/cu.usbmodem1421, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.Bluetooth-Modem, /dev/tty.SarelsiPhone4S-Wireless, /dev/tty.usbmodem1421, } / {/dev/cu.Bluetooth-Incoming-Port, /dev/cu.Bluetooth-Modem, /dev/cu.SarelsiPhone4S-Wireless, /dev/cu.usbmodem1421, /dev/tty.Bluetooth-Incoming-Port, /dev/tty.Bluetooth-Modem, /dev/tty.SarelsiPhone4S-Wireless, /dev/tty.usbmodem1421, } => {}
Uploading using selected port: /dev/tty.usbmodem1421
/Applications/ARDUINO/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avrdude -C/Applications/ARDUINO/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf -v -v -v -v -patmega32u4 -cavr109 -P/dev/tty.usbmodem1421 -b57600 -D -Uflash:w:/var/folders/sd/dzpfsctx5dlfdmt84z53xm3r0000gn/T/build4326096569440213265.tmp/Bridge.cpp.hex:i
avrdude: Version 5.11, compiled on Sep 2 2011 at 18:52:52
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2009 Joerg Wunsch
System wide configuration file is "/Applications/ARDUINO/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf"
User configuration file is "/Users/sarel/.avrduderc"
User configuration file does not exist or is not a regular file, skipping
Using Port : /dev/tty.usbmodem1421
Using Programmer : avr109
Overriding Baud Rate : 57600
AVR Part : ATmega32U4
Chip Erase delay : 9000 us
PAGEL : PD7
BS2 : PA0
RESET disposition : dedicated
RETRY pulse : SCK
serial program mode : yes
parallel program mode : yes
Timeout : 200
StabDelay : 100
CmdexeDelay : 25
SyncLoops : 32
ByteDelay : 0
PollIndex : 3
PollValue : 0x53
Memory Detail :
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
eeprom 65 10 8 0 no 1024 8 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
flash 65 6 128 0 yes 32768 128 256 4500 4500 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
lfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
hfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
efuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
lock 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
calibration 0 0 0 0 no 1 0 0 0 0 0x00 0x00
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
signature 0 0 0 0 no 3 0 0 0 0 0x00 0x00
Programmer Type : butterfly
Description : Atmel AppNote AVR109 Boot Loader
Connecting to programmer: .avrdude: Send: . [1b]
avrdude: Send: S [53]
avrdude: ser_recv(): programmer is not responding
avrdude: butterfly_recv(): programmer is not responding
processing.app.debug.RunnerException
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:125)
at processing.app.Sketch.upload(Sketch.java:1719)
at processing.app.Sketch.exportApplet(Sketch.java:1625)
at processing.app.Sketch.exportApplet(Sketch.java:1597)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2397)
at java.lang.Thread.run(Thread.java:695)
Caused by: processing.app.debug.RunnerException: Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
at cc.arduino.packages.Uploader.executeUploadCommand(Uploader.java:111)
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:123)
... 5 more
At this point it just hands...
... This might be a problem with avrdude I think?