The Maemo file manager has always been... less than ideal. Some have used much stronger negative language to describe it.

Don't worry. I guarantee someone will release a good file manager for the N900 with this functionality. There's a raft of good file managers out there that can handle all types of file shares, but they're just too big and heavy for the current generation of tablets. The N900 should be able to run them much better.

I'm personally looking forward to trying out full-blown Nautilus (the Gnome file manager) on the N900; I've got high hopes!