I've got an external backup disk that I use for backup. As it's living in a primarily Microsoft desktop environment, it's formatted NTFS for easy retrieval in case of failure.

/etc/fstab entry:
/dev/sdc1 /backup ntfs-3g defaults,nls=utf8,umask=007,noauto 0 2

Mounts fine.
/dev/sdc1 on /backup type fuseblk(rw,allow_other,default_permissions,blksize=4096)

Now I want to create a new directory ...
mkdir -p '/backup/Wednesday/user/projects/YEAR 10/01/06 Jan 2010'

mkdir: cannot create directory: `/backup/Wednesday/user/projects/YEAR 10/01/06 Jan 2010': Operation not supported

Now that's just plain not nice - I hate it when things just stop working for no reason. The nub of the problem was in this innocuous line in the system log...
Jan 6 11:48:14 server ntfs-3g[7536]: Not enough space to extended mft data: Operation not supported

The problem... the driver can't handle any more files. Max seems to be abour 54 million.

The solution...

1. Build the latest stable drivers from source
wget http://tuxera.com/opensource/ntfs-3g-2009.11.14.tgz
tar xfz ntfs-3g-2009.11.14.tgz
cd ntfs-3g-2009.11.14
./configure
make
( I had to 'apt-get install libattr1-dev' to get it to build ).

2. Uninstall the supported ntfs-3g packages
apt-get remove libntfs-3g31 libntfs10 ntfs-3g ntfsprogs

3. Install the new ones.
make install

I ran an ldconfig just to be sure everything's found.

Instant cure!

Hopefully debian will address this real soon now!