For me the motivation wasn't size, as I was satisfied with the partitioning, but I wanted MyDocs in a filesystem that preserves permissions (especially fed up with every file having +x when copied out of there).

I formatted it as ext4, changed a pile of scripts (there are instructions on page 18 of this topic), and actually remembered to change the ownership of the whole filesystem to the user before I even tried to use the camera — meaning I never actually experienced camera issues.

Right now I'm happily using my n900 with an ext4 MyDocs, no problems yet.

One thing I have to note though, since my uid on my work/home computers is obviously not the same, I had to do something to be able to write to MyDocs when mounted with mass storage. Best way to do that was with POSIX ACLs; man setfacl is your friend.