Just adding my two bits here.
I don't mean to be rude to those who don't believe the 4S to perform well in terms of sound quality, but from what I've heard (specifically, read in GSMArena's review of the latest iPhone: http://www.gsmarena.com/apple_iphone_4s-review-665p5.php), it has exceptional quality, offering a very neutral response wit little or no distortion/sibilance etc.
Then again, I'm no expert on audio equipment and the like, and I've no idea whether or not the readings in the test are accurate. Honestly, I'm just curious as to whether it's possible to improve on the performance of a mobile phone (smartphone, really) as a portable music player. After all, if it's the lack of codec support that's bothering you, there's always the VLC Player app.
P.S.
For the record, I'm the very proud owner of an i9000 Galaxy S. Voodoo Sound enabled, of course 
I'm only really considering an upgrade to the Galaxy Nexus... provided the sound quality is on par, that is.
EDIT:
Wow, I TOTALLY did not notice the last two replies. Well, to be honest, I just posted without reading all the replies to the thread, so... pie in my face :))
Looks like GSMArena's more popular here than I thought!
Cheers, everyone! Haha.
Edited by ZetsuBozu0012 - 11/3/11 at 12:59pm