What I was counting in the graph was transactions in the blockchain - surely speculation remains completely within an exchange and does not enter the blockchain at all? Daily transactions peaked at about 30,000 transactions/day in June, about the same time the price peaked on the exchanges. Right now there are about 13,000 transactions per day. What were the users doing with their bitcoins in June that they are not doing now?
Simon
Everyone was likely moving bitcoins to and from MtGox to sell / obtain them in their wallet. If people are just sitting on them now, then there are less transactions.