I switched over from Windows to Linux. I have an external drive that has basically just media files on it. Are there any advantages to converting this to ext3, or should I just leave it as ntfs3?
imho, leave it as ntfs. the support for ntfs across different OS is much better than for ext3, so you can use the drive when a buddy shows up and wants to impress you with his mac or his windows.
For external drives that will only ever be used with Linux, I always reformat them with ext3 so that extended attributes will be preserved. However, if the external drive will be used with multiple OSes then I use ntfs. Linux support for NTFS is very mature.