This isn't really specific to the Droid X, but I think putting this tip here would serve a lot of new Android users (like me!) well. I had an issue where every time I plugged my phone in to a computer or my car stereo via USB, it would go to "USB Mass Storage" mode, even if I selected "Charge Only"! After much putzing, I found a post in the EVO section of this forum that pointed out that DoubleTwist has a setting that automatically sets the phone to USB drive mode as a default setting. So, if you're getting "SD Card is Busy" messages even though you've set your phone to "USB Mass Storage" mode, check your DoubleTwist settings.