The Muslim Brotherhood is very much not in the driver's seat here. They're old and irrelevant, this is a moment for the young.
Muhammad Mursi said the group wants Cairo to revoke the state of emergency, dissolve the People’s Assembly and hold free and fair elections, amend the constitutional articles that led to vote rigging in Egypt’s last elections, hold presidential elections according to those amendments, and fire the current government and form a national unity government responsive to the Egyptian people’s demands.
http://www.phibetaiota.net/2011/01/nightwatch-extract-egypt-...
Though the return of Khomeini was definitely very much the catalyst.
Thirty years later, the situation in Egypt is different. The secular centrists and left-wing have a clear model of how to fill the vacuum. Even if they didn't before, Tunisia has provided one for them. There is little opportunity for the Muslim Brotherhood to step in as strongmen willing to make order out of chaos.
1979 Iran and 2011 Egypt are simply materially incomparable situations. There is a possibility that the MB will cause headaches for an emergent democracy, but their ability to seize control and establish a theocratic dictatorship is minuscule, at best.
Ok, that's a good thing then.
Is Iran financing them? Or do they have local support?
What are the relative proportions supporting these factions in the population?
Not sure on the popularity thing. I'd say plurality support, off the cuff, based on recent history, but a big portion of that support is "anyone but Mubarak" moreso than "sharia law rules". All gut feelings on my part though.
I've been researching them a bit further and it definitely seems they would command a majority of the votes at the moment so I really have no idea why people are so quick to write them off.
Agreed on the 'anyone but Mubarak', if this thing does not blow over Mubarak will be a very lucky man if he manages to even reside in Egypt, if he is forced out and does not flee abroad in time he's as good as dead.