Ok this thing with the mining adress was fun.
I wonder why he would do this. Withdraw 10 BTC an hour for 7 hours in a row? Why not 70 BTC at once if that is the balance of the btcguild account? Was it to see what it would do with the AM stock value?
I will try to explain (once more).
Here is a screenshot of my own BTC Guild account. As you can see from the tooltip, simply putting a value in the automatic withdrawal field means that BTC Guild will send that amount to your specified wallet whenever the balance meets or exceeds that amount. This will be checked every hour.
SO
We know This account has been active for quite some time now with many Th/s of hashing power. We've seen no evidence of a withdrawal until today. Which means all those coins were just stacking up over the last month or two. Someone came along and put 10 BTC into the auto-withdrawal field. The rest of what we saw was purely a functionality of BTC Guild's internal systems.
The answer to "why not all at once?" is: Because they don't want to manually log into all accounts every week/month and dump coins into the mining distribution wallet. Setting everything up to be automatic is the obvious choice in an operation of this scale.
So really, there's nothing to suggest hidden hash power at BTC Guild, and this was not an attempt at share price manipulation. The only thing left to speculate on is why auto withdrawal was just now turned on, and I think the obvious answer is that dividend payments are imminent. It's the only thing that makes sense.