There's a question raising every time I use some multimedia application on my nokia n900: why these apps totally ignore directory structure on my phone? Why do I need to browse through all 500 photos on the card to find some specific image which location in file system I exactly know? Directories are supposed to help me in this task - why ignore them? Same thing for music: it would be much more convenient to be able to play all mp3's in some folder, than to have multiple playlists that in fact duplicate the directory structure.
Is there some idea behind all that that I cannot get?

hit your title bar in the photo application and select by folder or tags or date.

For one, tags enable you to have media files in several groups at once instead of just one folder.

It's a pretty common concept among UI designers, not just at nokia, that end users don't "get" directories.

Try MediaBox?

For the Media Player, install the extra MAFW Source Plugins available in Extras-Devel. One of those plugins will allow you to browse the file system and play all tracks in a folder. It doesn't understand tags, though, unfortunately.