After weeks of the PSN being down services are being restored, it isn't happening all at once and purchasing through the PSN store won't be available as yet.
Although what's coming back online is
-Sign in for PlayStation Network and Qriocity services
-Online gameplay across PS3 and PSP
-Friends list
-Chat functionality
-Trophy comparison
-PlayStation Home
-Access to third party services such as Netflix
-Music Unlimited for current subscribers
A mandatory firmware update is available to restore functionality and gives you a chance to change your password. Now get out there and enjoy some online gaming!