This is a link to what's new in SkyDrive from the Building Windows 8 blog (from Microsoft). Read down to "Comments." NOTE the phrase "for a limited time" in the following paragraph from this page:
"We know that many of you signed up for a service that offered 25GB, and some are already using more than 7GB of storage. So, starting today, for a limited time, any registered SkyDrive user who has uploaded files to SkyDrive as of April 22nd can opt in to keep 25GB of free storage while still getting all of the benefits of the new service. (For users who are already using more than 4GB as of April 1, we’ve automatically opted you in to 25GB of free storage to avoid any issues.)"
This is a link to the Comparison Chart that compares the features and prices of (additional) storage, as well as the amount of free storage allowed, using SkyDrive, Apple iCloud, Google Drive, and Dropbox.
This is a link to The Windows Blog which shows a page full of posts about how SkyDrive works with various applications & devices (including Mac).