Current SkyDrive users have the opportunity to upgrade to 25 GB of free online storage. All you need to do is logon to your SkyDrive account and choose "Upgrade my storage".
Limited Time Loyalty Offer - SkyDrive (http://windows.microsoft.com/en-us/skydrive/loyalty)
Thanks for this notification! I didn't even know I was signed up for SkyDrive until I checked, so cool...I got to upgrade the storage limit. :)
Is SkyDrive something that could be safely used to back up hard drive files?
No, not for hard drive backup. It is restricted to "Ability to upload large files – up to 2GB – and folders using SkyDrive for the Windows desktop or SkyDrive for OS X Lion."
More info here: Making personal cloud storage for Windows available anywhere, with the new SkyDrive - Building Windows 8 - Site Home - MSDN Blogs (http://blogs.msdn.com/b/b8/archive/2012/04/23/the-next-chapter-for-skydrive-personal-cloud-storage-for-windows-available-anywhere.aspx)
and here: Windows Live SkyDrive - Online document storage and file sharing (http://windows.microsoft.com/en-US/skydrive/home)
Also of interest are Martin's articles,
Microsoft Skydrive Apps Released, Important Changes - Everything Microsoft | Leading Unofficial Microsoft Site (http://www.everything-microsoft.com/2012/04/23/microsoft-skydrive-apps-released-important/) and
How to Get the Best Cloud Backup / Sync Out of MSFT's new SkyDrive App - Everything Microsoft | Leading Unofficial Microsoft Site (http://www.everything-microsoft.com/2012/04/23/cloud-backup-sync-msfts-skydrive-app/)