I'm not the biggest fan of "the cloud." It might just be because I'm kind of inundated by use of the word. Or because cloud technology seems to be pushed at C-level executives who make choices that sound good dollar-wise but who don't necessarily understand the technical ramifications. Or because it's apparently still not possible to get a completely reliable Internet connection in the U.S., not to mention less developed countries. My philosophical objections to the cloud aside, there are certainly times when you need to store data remotely. I recently tried to back up my music to my external hard drive and Windows kept saying the drive was disconnected. I got it to work eventually (after some prying with a screwdriver and a little broken plastic) but it was a good reminder that if you really don't want to lose data, you keep local backups and backups somewhere else.
You could call that offsite backup, but marketing people hate anything that isn't expressed in buzzwords. So you get products named like the recently released Amazon Cloud Player. Cloud Player is actually a few different products—there's Cloud Player for Web and Cloud Player for Android, and both work from Amazon Cloud Drive (which has been around for a while). All the players and tools to use them are free, and your first 5GB of storage is free too.
Because Cloud Player is integrated with the Amazon MP3 store, songs purchased from there don't count against your storage limit. Also, until the end of the year, Amazon is giving a free one-year upgrade to their 20GB plan if you buy an MP3 album from them—even a $5 album—so for now it's a pretty good deal. After that, prices seem pretty steep; basically, $1 per year per GB, and you can only choose 20, 50, 100, 200, 500 and 1000GB plans.
You're not just paying for storage space, though. Unlike your typical business cloud deal, bandwidth is included. Amazon offers downloadable upload and download tools (though they're separate tools from one another) that work through your browser to make getting music into and out of your storage easier. The upload tool found my music quickly (it reads the playlist from Windows Media Player or, I think, iTunes) and was smart enough to tell which songs had already been uploaded, even if I'd changed their file names or MP3 tags. The files took about an hour per GB to upload to Amazon, which I think was a limit of my ISP, not Amazon—as far as I can tell, Amazon is allocating enough bandwidth (up and down) that your ISP is going to be the limiting factor.
Once songs are stored on your Cloud Drive, you can stream them to a PC or Android device. It streams the files at their original quality, so don't plan on listening to your music over a cellular connection—even on a pretty decent 3G connection, I got so much buffering that streaming was useless. On a good Wi-Fi or wired connection though, streaming works fine. You can also download the files (a much more practical option, if you're on a device with enough space, because you're going to have to transfer the same amount of data anyway, might as well keep the files locally). You have to install the Amazon MP3 Downloader to download more than one file at a time on a PC. In the Android app, file downloads are handled the same as downloading songs you've bought from the Amazon MP3 store, with fairly robust capabilities for downloading—you can tell it to only download when you're on Wi-Fi to save on your data plan, for example.
Speaking of the Android app, your Android device probably already has it, because the Cloud Player is integrated with the Amazon MP3 store app (which I couldn't remove from my Nexus One even if I wanted to—it's one of the pre-installed, un-removable apps). The app makes it easy to download all the songs from a certain artist or album all at once and to find and play streaming songs. It also can plays songs already on your device.
You can play and stream MP3s and AAC files on the service, but not other formats, including FLAC or any file with DRM. You can apparently use space purchased (or given to you as part of the buy-an-album deal) to store other file types, but I couldn't find any official documentation on Amazon saying so.
Overall, I'm happy with Amazon's cloud music storage, at least for the next year. Despite one recent, well-publicized outage, Amazon is a trusted player in the cloud and it's good to have my important files backed up on their servers. Once the promotion for 20GB free runs out, though, I'm going to look around for less expensive storage. And if I needed 50GB or more, I'd definitely be hesitant to spend the money Amazon's asking.
Pros: Easy to get songs to the cloud and back out; no loss of audio quality; well integrated with Amazon MP3 store; special offers make it inexpensive for now
Cons: Space beyond 5GB is fairly expensive; limited choice for amount of space to add; streaming capabilities useful in only limited circumstances
More Information: https://www.amazon.com/clouddrive/learnmore/