Like
balamw and
zephead, iTunes got me first, about a year or so ago. Until then, I had toyed with MusicMatch, WinAmp and RealPlayer on my PC, and none really fit the bill (although WinAmp was OK with its Geiss visualization). I ended up playing my music files individually through WMP-- I didn't bother with playlists. Besides, I only had a 6 Gb HD at the time, so I didn't have room for too many MP3 files.
So when I built my current PC, I began digitizing virtually my entire music collection, and I revisited the latest versions of all of the above, and iTunes won. I figured that if iTunes was done well, the iPod can't be far behind.
After a while, I got my nano, and the two just
worked. No convoluted configuration necessary. In Windoze, even.
That kind of forethought (and the arrival of Bootcamp) convinced me that my next computer will have that
logo.