I recently came across the service www.getdropbox.com . I immediately knew it was a service I would love and will use frequently. USB keys have been a must for almost everyone for many years. They were especially important to students though, because more than any other group of people I can think of, they use different computers all the time. Over the years to get projects done due to numerous circumstances I have used my laptop, home computer, parents laptop, friends laptops, home computers and finally literally hundreds of college computers. To do my work I always had to have my USB key with me. Naturally over this time some USB keys have been lost/ broken causing heartache and late nights redoing work. Dropbox solves this problem by syncing all your files online regardless of what computer you use to access site. It means that anywhere I've internet (including iPhone) I have my files.
This website got me thinking that the next step for iTunes or a possible way for a rival to get the jump on iTunes would be to allow the same thing for music. So that whatever device you used, as long as you have internet access you have listen to your music library. I think this would be amazingly useful. And in fact, when I did a little research I realized that someone is already doing this. The website is www.mecanto.com and you can upload as much of your music as you like for free.
If iTunes do not want to lose any market share, I think they should implement this service themselves ASAP. I recently downloaded an album from iTunes and on completion I was reminded to backup my music to CD in case the computer crashed, or else I would have to pay to download the album again! It seems quite clear to me that at this stage of the sales process a user should be able to backup the downloaded music online for a nominal fee (eg. €1), instead of having to revert to CD's which iTunes is suppose to be replacing.