Generally, I think 2.4 fixed most of my major problems with the X5, most importantly the 5800 song limit for the tag database. I do think there are some relatively easy to implement features that will increase usability greatly.
1. When scrolling through lists that may become large(files, artists, albums, etc) the skip buttons should go to the next letter, rather than just the next entry. I have close to 30,000 songs on my X5, and it takes almost 2 minutes for me to even reach the R's on my list of artists. I would like to be able to skip down to R entries by just hitting the lower right button a few times. Using the skip buttons currently doesn't have any advantage over using the click wheel to navigate lists, other than saving yr fingers some repetitive circular movement.
2. When updating the media lib, there should be an option for a "fast update". The device should store a timestamp of the last time the library was updated (probably two timestamps, one for last full update, and one for last "fast update"). It can then use this timestamp to only scan files which have a Date Modified that occurs after the stored timestamp. Like I said in my previous post, I have a relatively large media library, and every time I add an album, it has to take 20 minutes to rescan every file. This strikes me as unnecessary and inefficient. The only time I should have to do a full rescan of all stored files is when I have removed something from my SD card.
3. This is minor, but would still be nice. The player should have full Unicode support. I use the player in English, and any artists, songs, albums, files, etc. that contain international characters (specifically characters with an umlaut) have their special characters replaced with Chinese characters. Since it is typically only one letter, I can still tell what it is supposed to say, but it would look nicer if Blümchen, didn't have a random chinese character in place of the ü.
Both of these features should be relatively easy implementations, and would really increase usability for me, or anyone else who uses the X5 with a large library of music. I'd take on the task myself, but when looking through the X5 Custom Firmware thread, I realized that only firmware assets are editable, and not the actual code.