I know it's natural to hear the different instruments coming from different directions like in a live performance. To me, it doesn't sound better though. I like it better when the sounds are blended together. There are certain songs where the blended sounds appeals more than hearing them separately.
It's even worse if one earphone goes bad. Then, you only hear part of the music whereas in mono, you can still hear the whole set of instruments even with just one earphone.
Now, in games, I like the directional separation of explosions and gunfire. It helps me localize the bad guys.
When I rip my music CDs to mp3, I always rip them as mono, albeit at a high bitrate.