I have, I encode videos for a porn site (Not kidding)
Xvid and Divx both have their strengths, Xvid tends to have better picture clarity at low motion scenes, but drops bitrate through the floor in high motion (Unable to compensate for LONG high motion scenes. Think the Neo vs. smith fight in the second movie where he spins around on the pole and 'runs' on the smiths kicking them for a good example of high movement. So is switching key scenes REALLY fast over and over) while Divx tends to have great high motion clarity, but has lower resolution when running still frame shots (People talking, scene scapes etc)
Mov runs a -VERY- low bitrate compression, looks great but its not going to win any filesize awards. I tend to find it the most accurate and clean when you are makeing 2-3 disk encodes compaired to Xvid and Divx. a 1400mb mov will most often look better then a 1400mb Xvid movie, but drop that size down to 700mb and the mov will look like crap (Artifacts from hell)
ASF......toss up. It does what its ment to do (Streaming video) better then real media does, and without hogging your processor for all its resources, but its not going to win any picture awards.
Mpeg......ugh.....this has -WAY- outlived its usefullness and looks. It irritates me to no end that people release SVCD movies when a Xvid or Divx version would have looked a TON better and cleaner. If people want a SVCD go encode it themselves, don't make the rest of us suffer.
Now for problems (Yay!) Xvid is fast, fast fast fast at encodeing. It number crunchs like a SOB compaired to Divx. Unfortunetly in this speed crunching it mess's up sometimes, causing movies to freeze, crash, skip, invert (inverting was a BIGTIME problem for a LONG time that the developers actually had to go in and stick a "flip video" button into the playback settings so the movie would be in reality playing upside down, but you would see it right side up), desync, keyframe drop (When your screen looks like it has the last scene ontop of the one playing, and the colors don't refresh, thats a keyframe jumping ship on you and the media player dosen't know to change scenes/switch pallets) amoung others. Xvid is really try and work.
If you encode the whole movie in Xvid and it runs error free in playback, you scored. If not, you can go back and change compression/keyframe settings and try again, or give up, start up Divx and start the first pass and goto bed. Wake up in the morning (it MIGHT be done) and then set it to do the second pass while your at work/school. It takes a long time but Divx is more error free, and other people will have less issues with it then Xvid (Even if a Xvid runs fine on your computer, it might be messed up on everyone elses, so check before you start sending them out)
Thus ends todays lesson =) If you have more questions ask away
EDIT: Sorry for the old thread revival, just thought I should awnser this question as best as possible