I knew my GameCube memory card was dying, so I decided to buy a couple of cheap cards off of eBay (the official ones aren't produced anymore). The cards work fine, but there is just one problem: how can you get the data off of the dying memory card if it only wants to work half of the time?
And why are these cards so expensive? Even the generic cards go at nearly $0.50/MB, while these days you can almost get an SD card for $1/GB.
Use Dolphin and the memory card problem goes away. On my more powerful system, I used Dolphin (when the machine was working) and it's great. Easy to back up your memory card, Right click -> Copy, Right click -> Paste. (The correct way to get a working Dolphin build can be found here http://code.google.com/p/dolphin-emu/wiki/Linux_dependencies).