Is there a cap or soft-cap in % chance to find magic items? Should I stop stacking MF items at some point?
Old question already answered, but since the game has seen some changes since, an update seems necessary for the newcomers:
Currently in patch 1.0.7, the hard cap on Magic Find is 625% (300% soft cap + 75% NV stacks + 250% MP 10 on Inferno).
Starting in patch 1.0.8 however, the Magic Find bonus from shrines will be able to exceed the “soft cap” of 300% that players can achieve from a combination of their own gear and their follower’s gear. In patch 1.0.8 we’re also adding a buff to multiplayer games called “Strength in Numbers” which allows for a 10% bonus to Magic Find, Gold Find, and experience per additional player in a multiplayer game, up to a maximum of 30% in a four-player game. The Magic Find and Gold find bonuses of this multiplayer feature can exceed their respective 300% cap as well.
So after patch 1.0.8, if you have 300% Magic Find from your gear and your followers, have 5 stacks of NV (+75% MF), are playing on Inferno at MP10 (+250% MF), have a Fortune Shrine buff active (+25% MF), AND are playing a four player multiplayer game (+30% MF), you can hit the maximum of a 680% bonus to Magic Find. Shiny!
Keep in mind that this cap will be lower for if you aren’t playing on Inferno and/or aren’t using Monster Power level 10, etc.
Jay Wilson, Game Director of Diablo III, mentioned during a Best Buy Developer Chat that magic find will not be capped:
Guest-446: Will certain areas in Diablo 3 have different treasure classes like they did in Diablo 2 for finding higher items or does it just come down to how far you have progressed into the game and is there a diminishing effect of the amount of mf your character can have eg. like a mf cap?
Jay Wilson: I don’t really know how to answer the treasure class one, lots of areas have different treasure classes but we try to make areas relatively equal depending on challenge and monster level. MF is not capped, though.