According to the Wiki:
[Magic Find] Increases chance to drop high quality of items (Does not stack up with players anymore). Killing any enemy gives you +1 Passive Magic Find, which stacks up to 50, but all your Passive Magic Find is lost on death unless you have magic find in items or Patron.
However, I don't seem to find any relationship between the drops and the items I'm getting.
Maybe I just have too little Magic Find (73) to notice any differences.
Even with 125 Magic Find, as opposed to the 50 everybody's passive gives (after rammaging lots of items), I never seem to find piece of gear that has already been upgraded, or the chance of such gear increasing (has a star value on top of its rarity) or one of rarer qualities (Relics, Respendent and Shadow).
Note: To keep things consistent, I've experimented in Uber 3 difficulty for both attempts.