Upload to the shared Photo Streams can take a long time. Sometimes hours. Did the photos appear by now in the stream?
Is the iCloud status o.k. ( iCloud Support webpage)?
Did you share from your mac or from a mobile device? And where are you checking the stream? On your Mac? If you are uploading from a mobile device - is the battery fully charged? Uploading to the Photo Stream is the first that will be suspended, if the device needs charging.
have ypu exceeded any limits? Daily hourly upload rates? http://support.apple.com/kb/HT4858