Microsoft SkyDrive is decreasing the storage available to users from 25GB to 7GB. Existing users however can keep the 25GB but manual action is required: http://ludwigkeck.wordpress.com/2012/04/23/get-your-free-25-gb-of-skydrive-storage/

Also keep in mind that Microsoft Skydrive will become more and more integrated with Windows 8 and that they have also released an application (like dropbox) that also works for previous Windows versions. For more information check:

• http://blogs.msdn.com/b/b8/archive/2012/04/23/the-next-chapter-for-skydrive-personal-cloud-storage-for-windows-available-anywhere.aspx
• http://www.winsupersite.com/article/windows8/skydrive-service-update-windows-application-mobile-apps-142906

UPDATE:

Google drive has also launched and also dropbox is making improvements to its service. Before deciding to use any service however, compare their terms of use: http://www.theverge.com/2012/4/24/2972228/cloud-storage-terms-of-service-comparison-avoid-google-drive