To begin, an awkward property unique to the Gen II Pokemon games (as far as I know) is that when the save batteries are dead, the save file actually lingers for around 45-60 seconds. As soon as a few minutes after I heard of the MMC, I theorized that you may be able to exploit that property to take the save off of the cart, or put it back on and reset. So naturally, after getting my MMC in the mail, it was one of the first things I attempted, and despite what I thought was likely, my idea actually worked! So you can use the MMC to negate the effects of a dead save battery on Pokemon Gold, Silver, and maybe Crystal (I don't know if it possesses that effect as well, as I bought my copy with a fresh battery). If I am the first to discover this, I will be very amazed.
EDIT: When poking around, I have seen a few people mentioning this, so I am not the first to discover it :(