When considering other free offerings -- especially Live SkyDrive's 25Gb -- Google may not see a lot of customers for their storage business until they rework their pricing plans.
Apple MobileMe: Pretty, But Expensive
Apple is all about controling the customer experience. Always.
Once you get that, you will understand the approach to MobileMe, a file storage/syncing offering that also syncs messages and calendar information for $99/year. This is a very rich tool that really does a good job seamlessly syncing between Macs, Windows PCs, and iPhones. Like most Macs and OS X, it's pretty and slick.
But looks aren't everything. If you choose to participate in MobileMe, you'll only get 20Gb storage (shared with files and e-mail) and, interestingly, a 200Gb/month data transfer limit. A transfer limit like that should not really affect anyone, but it's curious that Apple feels the need to even specify it. If you want more, you can upgrade to the family pack for $149/year, which still gets you 20Gb of space, but with four e-mail accounts, each with an additional 5Gb storage.
If you are a devoted Mac user, this might make sense, but even then, your money is better spent on Google, where you could get 10 times the space for half the cost or, again, the SkyDrive option where 25Gb is free.
Ubuntu One Not For All Yet
Linux users should not feel too left out; there's a dedicated personal cloud service for them, too. Canonical, the makers of the Ubuntu distribution, has the Ubuntu One service, which offers file, contacts, and message syncing for users of Ubuntu and ... apparently no one else. Not even other Linux users.
That sort of limitation is really very odd coming from an open source company, though apparently plans are in the works to port the Ubuntu One client to Fedora, another popular Linux distribution, as well as Windows and OS X. Still, unless Canonical can shift to cross-platform soon, they may be too late to the party.
If you are an Ubuntu user, you will get pretty seamless file, messaging, and contact synchronization, as promised, and 2Gb of free storage. There's even syncing for Tomboy, a sticky-note app. This kind of integration is really needed in the Linux operating system, and Ubuntu One has definitely set that bar for this platform.
If you want more storage, though, be prepared to pay -- a lot. 50Gb of space goes for $10/month, or $120/year. Not as expensive as Apple, but close. Certainly more than Google's price structure.
It would be great to see a service like Ubuntu One take off, but right now it's holding itself back as a cross-platform solution.
Not a DropBox in Bucket
DropBox is pure file sharing. No fancy-schmancy messaging or app integration here.
This cross-platform service nicely integrates with your operating system's existing file manager.