Senkwe Chanda has found the secret to Spaces success! The whole entry is interesting, but I like this part the best:
What’s driving it is actually pretty simple and is a stroke of pure genius (assuming it hasn’t been done before), MSN Messenger integration. You are updated via Messenger whenever one of your contacts updates (or indeed creates) his/her Space. All it takes is one ADD inflicted prepubescent teen to create a space and the snowball effect kicks in via his/her Messenger contacts list. Killer.
Read the whole thing.