Here it is! This is proven to Blizzards Magic-Find system.
STIKY THIS!
Make sure you read the whole thing. Ask me any quetions.

Magic Find|Magical|Rares|Set Items|Uniques *
-----0% | -0%--*-- 0%--*--0%--*--0%*
---100% | 100% * 100%* 100% * 100%*
---150% | 150% * 146%* 145% * 141%*
---200% | 200% * 185%* 183% * 171%*
---250% | 250% * 220%* 215% * 193%*
---300% | 300% * 250%* 242% * 211%*
---400% | 400% * 300%* 287% * 236%*
---500% | 500% * 340%* 322% * 253% *
---750% | 750% * 412%* 382% * 280% *
--1000% | 1000% * 460%* 421% * 295% *
--1200% | 1200% * 494%* 448% * 305% *
--1500% | 1500% * 520%* 468% * 312% *

* The actual % that is applied towards finding each type of item. Magical is full, Rare/Set/Uniques are less.

How much you want to wear should be based largely on these percentages. More always helps for magical items, so if you have 1000% MF you'll get incredible amounts of blue items. The weapons might be useful, but the odds aren't good. Charms and Jewels are not boosted by your +MF%, so this doesn't help with those. Best way to find more of those is to kill more things. Rares increase pretty well up to 600% MF or so, but Set items really slow down past 400 or 500%. Uniques are much the same, but even worse in the diminishing returns. Notice that from 300% to 1500% only increases your Uniques MF% by 101%.

If you can get to 250-350% that's really all you need, in terms of finding Sets and Uniques at an increased rate. More after that generally doesn't make enough of a difference to be worth the equipment sacrifices, especially if you are playing Hardcore.

STIKY-THIS_STIKY-THIS_STIKY-THIS_STIKY-THIS_STICKY!