I've trying desperately to connect my Charge to a 2010 iMac (snow leopard) and the device does not seem to ever boot. All it does it "charge" (haha..) through the USB and does nothing else. Tried restarting both Mac and Device, tried every imaginable combination of USB setting with debugging on/off, the device does pick up on bluetooth, not that it helps me any. Disk Utility shows no other devices, and there are no USB on/off notifications found on my pull down menu as decribed on other forums discussing the same topic.
I've installed iTuneMyWalkman and Salling Media Sync in hopes that the device would sync and pick up on my computer. No luck finding drivers online in case that was the problem as well.
I have a 2010 iMac formerly running SL. There is only 1 USB port that will properly recognize the phone. Try the USB port right next to the firewire port on the back of the iMac. If that one doesn't work try the others. It won't work thru the keyboard or a USB hub. Also, make sure you use a good USB cable. Mine works perfectly and has worked consistently since I figured out the port.