Yeah, some SD cards tend to somply poop out. :| I had a 54 MB card a while ago (it didn't hold much) and eventually it just locked itself.
Nothing lasts forever I suppose. Oh well. It had a good run; three years is pretty good. I think I had it before Brawl even, and I used it to store all my custom stages.
Also one of my flash drives -- and 8GB PNY one -- pooped out on me as well. The issue with it is when I insert it into my USB port and attempt to go into its root it says there is no drive inserted even though there is. I had to get a new flash drive which was a 16GB SanDisk Cruze for my 18th birthday present.