Here are the reasons I like a hard-drive based portable MP3 player:

• I like music
• I possess a lot of music, overwhelmingly in electronic form only
• I am not good at forward planning
• I am ordinarily too busy to spend long periods listening to music
• I have long periods of "downtime" when travelling
• A portable player mean I can make use of this down time
• The large capacity of a hard-drive player means I don't have to think about what music I want to listen to in advance and burn it to CD; I can select it on the go, and as a bonus, I can listen to all my music at once.
• I also don't have to carry a load of CDs around, and I don't have to change discs all the time

Listening to music, in general, makes me happy. Thus, my iPod has turned more than 2 hours of every weekday that were previously mood-neutral at best into mood-positive hours. That's a significant improvement in my quality of life, and it is available only from a high-capacity portable music playing device.

Why I prefer my iPod to other available devices:

• It has an extraordinarily well designed user interface, from hardware to software -- it is easy to use, at every stage, from filling it with music to ordering and sorting that music to playing that music, skipping through it, finding it again, and picking up where I left off. It's adaptive: it learns what I like, how I listen, and it continuously improves its knowledge.
• In addition to being a highly capable portable music device, an RSS feed reader app called iPod Agent that uses its "notes" features has also turned it into an adequate portable blog-reading device. Several hours of my day used to consist of me listening to music while reading blogs, and not getting much done. Now I do this on the tube, and as such I am noticeably more productive all the rest of the time.

Any further questions?