Amazon has announced Cloud Drive, essentially a hard drive in the cloud, and 5 GB of free storage to get you started. Aside from file storage, Cloud Drive is specifically intended for storing your digital music collection which can then be played back using Amazon Cloud Player (for web and Android).
Of course, unless you are buying new music from Amazon (which will get deposited right into your cloud drive), this requires that you upload your entire music collection, and so Amazon created the Amazon MP3 Uploader. And the MP3 Uploader (which also uploads AAC files)? It's a web based Adobe AIR app built using jQuery.