In it's current state the Limewire Library tab needs a lot of work. I'll list a couple of the features that I think would greatly add to it's capabilities here.
1.) Organize files based on type, rather than physical location. For example, when Limewire scans shared directories have it organize the files it finds into Audio, Image, document, Video, and Software based on their file type. This makes it a lot easier to find music files that are stored in a physical directory along with other types of files.
2.) A search mechanism. I personally find it rather hard to find a specific file I'm looking for in the existing Library system, so I believe that giving the user the ability to search his/her shared directories through Limewire would make it much easier.
Note: I got both of these ideas from Ares, if you want to see what I mean download it from softgap.com and look at it's library. Quite nice.