We were on the 2/7 Eastern Magic. DD LOVED The Stack and can't wait to go back.
They have about twice as much space as was previously available in Common Grounds, with greatly enhanced video abilities. There are actually 2 main rooms, so one group can be involved in activities, dancing, whatever while another group is just hanging out.
She says the 20something counsellors are teen wanna-bes, but had only good to say about them. Really enjoyed the Wild Side excursion on Castaway too.
There are really great planned activities, but you don't have to do them. You can just hang out with friends, listen to music, etc. A party is planned every night with a different theme for each. Sodas and smoothies are available (for a fee if not on soda package). There is also a list of activities that can be done at any time--the kids just have to ask the counsellors.
Also, the phone number posted in the Navigator is correct, even though it looks wrong. It has one more digit than any other number on the ship, as they have run out of 4 digit numbers. I ran up there twice as I thought the phone number was wrong.