"focus group" & "to rock the joint"

Hello everyone,

I've got 2 questions referring to the text by Joe Klein about Sarah Palin's speech at Tea Party Convent:

1) what does 'focus group' mean in the sentence: "
she does folksy far better than George W. Bush or any of the other Republican focus-group populists ever did."?

2) what does it mean "to rock the joint"?

Here is the whole paragraph to give you the context:



"How's that hopey-changey stuff workin' out for ya?" Sarah Palin asked the anti-élitist Tea Party élites — those who could pay $549 for a ticket — gathered in suffocating self-righteousness at the Opryland Hotel on the first weekend of February. It was classic Palin, a brilliant line, brilliantly delivered: she does folksy far better than George W. Bush or any of the other Republican focus-group populists ever did. It was the signature line of her speech, which rocked the joint — and then, slowly, began to rock the national political community. The speech was inspired drivel, a series of distortions and oversimplifications, totally bereft of nourishing policy proposals — the sort of thing calculated, carefully calculated, to drive lamestream media types like me frothing to their keyboards. Palin is a big fat target, eminently available for derision. But I will not deride. Because brilliance must be respected, especially when it involves marketing in an era when image almost always passes for substance."