Given their strength and grass-roots orientation, and the fact that they will rise or fall on the will of the country at large, not the rebels in Tahrir, it would be foolish to say so. Issandr El Amrani thinks they have suffered a setback, and I'm frankly hoping he's right though it's not my choice, but Egypt's, to make.
I think Issandr has it right:
But their leadership has failed them once more. Once again the Muslim Brotherhood has shown that its basic essence has not changed: just as its leader in 2009 said he had no problems with a Gamal Mubarak presidency and had much respect for Hosni Mubarak, just as they rushed ton negotiate with president-apparent Omar Suleiman in late January, just like they preferred to cut a deal with the military in the transition's early days and accepted a slapdash referendum and constitutional declaration, the Brothers are once again swimming against the prevailing tide of the Egyptian people. They prefer to negotiate for their own maximum advantage rather take a principled position.
I often think the Brothers' biggest problem is not that they are fundamentalist, or out of touch with the Egyptian mainstream, or too radical. It's that they are perceived, rightly, as schemers by average people. It's true of their leaders, at least, and it's what has made so many bright young people leave them in recent years and so many others doubt their intentions.
Of course, things are moving quickly. Perhaps when the end game finally comes the MB will have had it right all along. But they made at least a tactical error.