Just to throw this question out there because many people will want to know, which of these various services are accessible natively by those running XP or Linux on their desktop? (and I am not referring to being able to use the services from a web browser)
The SkyDrive app will not install on systems running WinXP. And as far as I know, no app to offer Linux desktop support, either.
Also missing from the chart is SugarSync, which offers 5G free, allows sharing of files and folders, public sharing through links, and some other nice features.
I am actually using SugarSync to host downloadable files for one of my Blogger based sites. While it is not as seamless as using Dropbox and requires a little bit more fussing to make a file public and then get the links to publish on my site, it does have the advantage of letting me know the total number of downloads, which is something Dropbox doesn't do. That alone made the fuss worth it and why I switched from using Dropbox links to the same files.