Interesting. In my very quick testing just now, typing letters definitely moves to the files starting with those letters, except for "r" and "n". Those two crash it. It's really good to know that you are planning to eventually add proper search functionality. symfonie is shaping up to be the best music player on the N900!
I mean that symfonie has no icon in the application menu (at least not for me) and because of this it is displayed only as a blue dot (default icon for Maemo applications without an icon). It would be nice if you could add one...