I payed(34$) for the full NTFS driver from Tuxera, the free version was not able to safely eject NTFS disks.
Update: starting with Lion, you'll not be able to share the NTFS drives even if you use NTFS-3G or Tuxera NTFS for Mac.
It may be a good idea to reformat your drive to EXFAT in order to overcome these issues. I know it's a real pain and time killer.