i'm used to use the playlist for redefining and organising my library, while the search list for me has been mostly just a list of searched files. still i have always used them with similar columns settings which means they both need horizontal space a lot. i'm really disappointed with the 4.x user interface. too messy after the 3.x, though it looks almost same at the first glance - but it isn't the same in practice..
also the search line should be horizontally scalable, and the toolbars lockable (not only in party mode, which i personally never use for the user interface is "sacred" to me)..
the reason i switched from winamp to mediamonkey originally was the MM's efficient database functionality yet simple user interface, while winamp had screwed up their database functionality completely by that time and don't know if it still works. please don't sell out and screw up MM totally. my music library is a real collection to me, not just a bunch of hits of the week, and that's why a database that allows me to organise my music and do refined searches by multiple criteria is very essential to me.
altogether it seems that the user interface design is not one of your strengths. i love the database functionality, but since the MM 2.x the user interface has been going down. too much new stuff gets in the way of the previous simple and clear functionality. i think the new features should be more or less optional, or you should probably split the program to separate sections so that music, videos, whatever will be totally in their own categories so that music lovers wouldn't be bothered with the other media non-sense.
well, i'm switching back to 3.x for now, and just wish that you wouldn't bare your program with too much fancy non-sense and other unnecessitites in the future. backward compatibility is essential in its every aspect, including the user interface - not to mention the settings and other previously stored user data. be careful how you develop the program, the music library really doesn't need that much of the new fancy gimmicks, but sustained and refined functionality. please consider that..
all in all, you have a great music
library database program, so why not keep it that way (on the basis of 3.x)..