Amazon Cloud Drive, Google Music Beta (Cloud), Apple iCloud are the buzz words from the recent weeks. In short, these are attempts made by each of the three tech titans to free you from your plebeian PCs and home servers allowing you to move your content (mostly music) to "cloud" servers hosted and maintained by them.
The idea is simple, upload your music (and other content like contacts, emails, photos in the case for Apple iCloud) and you can get access to said content from anywhere as long as you have internet connection.
Amazon's Cloud Drive and Google Music Beta offers good integration with Android for now and the upcoming iCloud is going to be integrated with iPad/iPhone/iPod Touch's iOS 5.0. In terms of capacity, Amazon's Cloud Drive is free up to 5GB (limited time offer provides a free upgrade to 20GB for 1 year and automatically downgrades if you don't want to pay the $20/year fee thereafter) while Google's Music Beta limits to 20,000 songs (no more than 320kpbs sound quality) and Apple iCloud is capping out at 5GB for it's free account.
In terms of playback the content you have uploaded, Amazon and Google offers some what of a streaming/caching service versus Apple's approach of wireless download the content to your phone. As far as uploading your content to the cloud, most of the offers some type of upload application for Mac and PC (Amazon Uploader, Google Uploader) so you can quickly transfer your music from your local storage; I presume Apple will make iTunes function as an uploader upon release. Amazon MP3 Music Store and Apple iTunes also offers direct transfer if you purchase music from them. Whats crazy is that Google even offers some free songs to be added to the account during setup (I would add as much as you can since I could not figure out how to add more after initial setup, see reference).
Bottom line: Cloud storage is the future; local storage is a thing of the past. Most techy nerds will still want to hang on to terabytes of storage at home for bragging rights and being a control freak, I don't blame them. However, the future of computing is all about having the flexibility of accessing your data and content on the fly without having to worry about maintaining the connection or security of your own server. Music seems to be the overarching theme that initiates the cloud conversation. Regardless of content type, it appears every tech titan is coming after cloud storage solution. Ever since the introduction of Gmail account, Google have successfully entered the non-music based cloud services (Picasa for Photos, YouTube for Videos, Email/Contacts/Calendar/Docs, IM/VOIP). From my viewpoint, Google's integration with Music beta will further secure it's inevitable future dominance of the mobile marketshare via Android or Chrome OS. Where Apple and Amazon have advantage is its network externality of its music stores. Regardless, the cloud race is now officially on!