not "problems", it is just very slow.
The Kindle Fire also just quits responding when on USB. So, if you don't get it transferred quickly enough, you have to yank the cord (which cancels the xfer, finally) and plug it back in and try again (doing a 'skip' on files that exist). Also, Win7 refuses to let me use Teracopy with the Kindle Fire (it manages copies, does verifies, etc - but won't work with the Fire). Yes, you are supposed to eject it first -- but there isn't an eject option on the Fire (a lot like the Kobo reader and the Sandisk MP3 players - you just have to make sure it isn't being accessed and unplug it, as there is no Eject and it doesn't show up in the usb devices to eject, as well).
Since transferring the content I had will probably take over an hour, I've been putting it off (it took three days of copying to get it backed up - apps, magazines, etc).