Yesterday, Amazon announced Cloud Drive, which is essentially a consumer streamlined version of S3, their online storage system. The sweet part is how it works with music. You can upload your junk up there, and you can then stream it from anywhere with a Web browser. There's an Android app for it too. So it's like Pandora, only your own stuff, that you control.
I was already using JungleDisk to backup all of my music in S3, so using this makes sense for me. I bought a $50 account (50 gigs) for the year, and started uploading it last night, while deleting the music backup from my S3 bucket. You pay for whatever you use on S3, so the cost change is essentially a wash. They have an uploader app (OS X version, in my case), and it scans your iTunes library, compares to what you've already uploaded, and sends it all up. It even imports your playlists.
The browser-based Cloud Player is simple, and just works as you'd expect it. Your playlists appear at left.
So what's the killer app here? Well, it would be more killer if there were apps for iPhone and Windows Phone, but I doubt it will ever happen for iPhone. WP7, I think, has a fighting chance, but it won't make sense until the audio playing background task is enabled in the later-this-year update (I think that was one of the things they showed in Barcelona). But phones aside, you can play your crap where ever there is a computer... at work, airport wi-fi, hotels... it's pretty awesome. And if your house burns down, with all of your iPods and phones and computers, you don't lose anything.
I've always felt that this was ultimately the way to do it, I'm just surprised that it exists already. The company that sells books figured it out first. That's nuts. In any case, it gets my stamp of approval. I dig it.