I am guessing it was the file system format. I changed to ext4 and whenever I try to mount it on N900 like so:

mount -t ext4 /dev/mmcblk1p1 /media/mnt

I get:
mount: mounting /dev/mmcblk1p1 on /media/mnt/ failed: No such device

If I remove the fs-type or provide a wrong fs-type, I get:

mount: mounting /dev/mmcblk1p1 on /media/mnt/ failed: Invalid argument

Now, I guess I'll try with ext3... Strange that ext4 works for you. Or I need to install some other e2fsprogs package.