3ivx D4 will play just about any of the various DivX iterations within QuickTime, but due to a bug in QuickTime, won't play any MP3-encoded audio without a lengthy conversion process (which means double the hard drive space). The new files are not Windows friendly! Too bad a good 80% of DivX files out there use MP3 audio.
DivX for Mac plays DivX 3.11, 4 and 5 files flawlessly, with full audio support (apparently they found a workaround for the QT bug), but will refuse to play any XivD files -- XivD is the open-source DivX spin-off, so the DivX people are understandably trying to quench it. Unfortunately, more and more files these days are XivD.
The solution: just install both! 3ivX's plug-in will take over for all of the video duties, while the DivX plug-in will step in to play MP3 audio tracks. After you have both plug-ins in your ~/Library -> QuickTime folder, almost all DivX-ish files will play, convert, and edit seamlessly.
Perfect! Now we just need Ogg, Matroska and WMA/WM8 support in QuickTime and we'll be all set!

