Beeplance
macrumors 68000
This, seriously. I have a 64GB model, and while it's useable for the most part, I can't believe I had to wait for the Music app to bring up a list for 50GB of music.
Perhaps you've updated your 4th gen to iOS 6? Mine is still on 5.1.1 and have takes only 0.5 second to load up my music library. From the numerous accounts I've seen, for most part iOS 6 doesn't run that well on the 4th gen, mainly due to the shortage of RAM.