Iran 30 years ago and Egypt last week are two completely different revolutions.
In Iran, the military cracked down on anti-government protesters brutally and repeatedly. They'd drive them under ground only for the movement to resurface, better armed and more extreme. The process took nearly two years, before protesters finally destroyed the Iranian military and security forces, forcing the dictator to flee. By the time the dust settled, the country was in a state of anarchy ruled by angry disorganized mobs. Religious Mullahs filled the power vacuum and seized power by default.
In Egypt, the military acted with restraint, only intervened to prevent violence and vandalism. After a couple weeks of mostly non-violent protests, the military was not only intact, they remained well organized, disciplined and also had popular support. Egypt never experienced a power vacuum. Now Egypt's military will oversee the transition to a democracy. We'll see if they allow a free democracy or play some sort of shell game and force the protesters to return to the streets. I expect the US will continue to play a positive role in the back ground, and I'm hopeful Egyptians will have free and fair elections.
If Egypt becomes a representative democracy, then the MB will play a role in a future government based on how well they do in the upcoming election, but they are hardly in control now and unlikely to gain absolute power in the future. The people behind this movement didn't risk their lives to replace one autocratic system with another.
What we are seeing now is shameful scare mongering by Israeli apologists who fear dealing with a free Egypt. They really don't care about freedom or justice when it comes to others. They'd rather that Egyptians remain oppressed and suffer human rights atrocities as long as they can pull the strings of a compliant dictator.
What these people don't realize, is that the status quo in Egypt was unsustainable. If the military cracked down on the Egyptian people as they wished, eventually the people would have won eventually after much death and destruction. But the military wouldn't be around to guide the transition process and there is a good chance the MB would fill the power vacuum, just the Mullahs did in Iran 30 years ago.