MF% INCREASES your odds of having a Magical/Rare/Set/Unique drop. Yes, you can still find these WITHOUT MF, but it's far less often, ergo, you have to be a lot luckier to find the same items WITHOUT MF than WITH it.
Also, it always seems the higher level you are, you're always luckier... But the main idea is: mf does increase your chances of finding Magical/rare/set and unique items at the cost of the ineffectiveness of the magic find items. The better equiptment you have (not mf), the more enemies you kill (faster rate) causing more chances of decent drops. It might actually even out at some point but that usually has to do more with bots or fiends doing 24 hrs of strait mf runs.
The higher level you are means better items drops. Look at a level 70 blizzard sorc compared to a level 85. Level 85 gets more high level and lower level stuff.