Their warranty conditions (http://www.transcendusa.com/Support/Warranty.asp) seem to be pretty clear. I'm pretty certain they won't invest the effort in proving that you "abused" the card in an unspecified fasion.

The question (for an N770) is more if MMC cards will still be in production, say, 5 years from today.

I have a related question: is there a cookbook for swapping to the MMC when the MMC is mounted as root?

I am not sure that article is helpful. First it is for flash hard drives and the size in the test was 64GB. Second, I looked up the durability of my Kingston 2GB MMC Mobile card - it appears to to be 10,000 writes per physical sector which is for multi level flash which I believe it is - otherwise it is 100,000 writes not millions as the article specifies.

This has been answered many times on these forums, and on the maemo website.

Even if continously writing on the same spot of the mmc card all the time, it will take you many years to wear it out in any noticeable fashion.

There's a lot more to media writes than just file updates. Consider just 'atime', which is 'last time of access', a *nix filesystem mounted with default mount options will write to the disk every time you access a file, that is, when you read it. So you only have to keep reading the file, and you'll write to the disk. For FAT filesystems there are issues with the directory updates, I remember reading an article about flash card wear levelling a couple of years back (possibly on wikipedia), and it was pointed out that if it weren't for wear levelling you could easily reach the 100000 limit in a short time just because of FATs inefficient directory handling. (I didn't find this article when I searched on wikipedia right now, so it could be that I read it elsewhere, maybe handhelds.org)

Oh, and if your SD card is formatted as ext2 instead of FAT it's probably a good idea to mount it with the 'noatime' option. Very few programs need to know time of last access (as opposed to time of last update), so this will reduce writes as well as improve speed.

Maybe it was this article (164Kb pdf).

Thanks Milhouse,
I think it was another article I read back then, but I suspect it was referring to the one you pointed to. Very useful. Thanks for the link!
An interesting excerpt:
".. so the FAT table is updated 4096 times while writing an 8MB file." (this is with FAT16 and a cluster size of 2KB).
Without wear levelling flash wouldn't be useful at all.