I think the term "cloud" is going to get overplayed (can't we just call it the Internet?) but Amazon has taken the bold leap of offering us a way to access our music online, wherever we go. Apple was supposed to be in the running for this some time ago, especially after they purchased the web music company LaLa. Their service never transpired so the idea of accessing your iTunes music collection online may not be arriving soon, although one should never count Apple out. So here's the Amazon Cloud Drive.
The details: Access your music anywhere that you have Internet access. You can also stream your music via Android (no mention of iPhone, of course.) 5gb of free storage, more storage can be purchased up to 100gb. Any MP3s purchased through the Amazon store do not count toward your initial free 5gbs.
Slightly jerky UX problem - Uploading was smooth and quick although you can't just click on a music folder to upload it, you have to enter the folder and select all the songs to upload them. They appear at first in the Cloud Drive as just a list as if they're not in an album folder, but when you click play they appear as an album.
[Update] If you purchase one MP3 album from the Amazon MP3 store you get a free 20gb storage upgrade for your Cloud Drive.
I'll be messing around with the Cloud Drive for a while so I'll update this post as necessary. Details here
Here's some screenshots of my first use of my Amazon Cloud Drive.