you should be able to do 48-480GB of writes until the nand breaks but that's only in theory with the nand controller perfectly using the pages.
Each page can take 195 to 1950MB of writes.
The main problem will be the area where the NAND stores the filesystem since that area is static and is not mapped to other clusters (it has 256 clusters -> 8*256 = 2048 pages -> 2048*2048 = 4194304 = ~4MB) .
And these change everytime the FS is changed, basically all the time!
The NAND is stressed more than people think, many games store temp files on the nand each time you run them (i.e. SSBB around 20MB, most of the "rebirth" Wiiware title copy their music on the /tmp dir aswell, hell knows why...)
Each time you change the disc the system menu creates a new cache.dat on the NAND.
You can better be safe than sorry since once IOS runs into FS troubles it runs format to fix it. *facepalm*
( 262144 pages á 2048 bytes = 512MB, each page can be written 100000 to 1000000 times )
