Normaly, it should save hiscore, if you wait a little on the title screen, you'll see them. By default, I use the pandora's user login for the username as input entry was not working... But I saw that Notaz fix that in the lastest firmware, so in future version you'll can enter different username for your score.
Difficulty level change how many time you gain with combo, but it need tweeking, or bugfixing. The easy mode is too easy, I think somebody quite motivated could possibly block the score in this mode.
In legend, you gain not much time with combo and between level, but maybe too much it seems
A game mode with no time limit can be interresting. Though I never had a board with no valid move, so indeed, maybe you might playing forever
I plan other mode in the future, for exemple a puzzle mode. I have also a mode where the pattern to collapse tile is not a line but a triangle, and a mode where the both are valid (it a combo fest in this mode). I'm thinking also of a tetris like mode with falling gems.