3 things:

1) I have checked 5 PAL DVDs and thay are ALL NTSC now, so it seems it changes almost every APL to NTSC.

2) Another thing is it changes the MPEG flag from MPEG2 to MPEG1

3) And finally if you have subs on a 16;9 movie that has been changed into 4:3 it is almost unwatchable cause the subs are still in 16:9 and changing the aspect ratio with IFOedit doesn't do a thing to that.

Movies tested:
James Bond's the world is not enough. (but most james bond's DVDs are wrongly Authored)
The godfather I II and III
Jurasic Park I
Resident Evil