So being a Linux-only kind of chap, I went through the process of re-formatting my MicroSD as ext3 and having the N900 mount it automatically. I forget the thread but with a bit of tweaking it's possible.
Performance seemed better and it was nice being able to store symlinks & files larger than 4 GB.
But I could not find a way of solving the UID/GID permissions problems. The N900 user has one UID, my desktop has a different one, files & directories do not always have universal read/write access and I don't want to permanently change my umask on either N900 or Desktop PC. I also don't want to manually change permissions of everything I copy back & forward. So until there is a filesystem flag to ignore ownership, I'm back to crap old FAT32 for my Linux-to-Linux transfers .