24p, btw, is not a garantee for smooth playback. it never has been.
iro Planet Earth as mentioned specifically it did solved the 2:3 pull-down judder on the HD-DVD versions.
24p mode should guarantee smooth playback if the judder is as a result of 2:3 pull-down in the NTSC 48hz to PAL 50hz or 60hz conversion. If the judder is still there there is a problem with the source or display. Either the implementation is shoddy or the set-up is incorrect. Both source and display (TV or PJ) need to be able to cope with 24p and sometimes the TV needs a special mode enabled in order for it to work, e.g. advanced mode on Pioneer's Cinema mode.