My friend who did his thesis on Iran said the police staying neutral was one of the key factors for the success of the Iranian revolution against the Shah. A BBC roundup:

Iran's most senior dissident cleric Grand Ayatollah Hossein Ali Montazeri calls for three days of national mourning for those killed in street protests, Reuters news agency reports

* Former pro-reform President Mohammad Khatami calls for the release of detained activists

* Iran police chief Gen Esmaeil Ahmadi Moghaddam warns any further unrest will be confronted "decisively"

* Iranian officials again attack the UK for "interfering".

More detail on the police, also from BBC, and the reaction of the Iranian people:

Iranian authorities have deployed thousands of security officers on the streets of Tehran, after a week of mass protests over a disputed election.

On Sunday, thousands of security officers were out on the streets but protesters stayed away.

The BBC's Jeremy Bowen, in Tehran, says many residents of northern Tehran could be heard shouting from the rooftops "death to the dictator" and "Allahu akbar" on Sunday evening.

The chants have become a popular form of protest, and our correspondents says men, women and children joined in and Sunday's chanting was much louder than on previous days.

And from Jeremy Bowen on the BBC's blog, it looks like the split in the government elite is real and becoming more likely to last:

The strong show of force for a second day meant that there were no demonstrators on the streets but that doesn't mean the crisis is over. Far from it. The splits in the country and in the leadership are too deep for that.
Neither side shows any sign of giving in. The Supreme Leader Ayatollah Khamenei has demanded that all the Iranian people accept an election result he insists was fair.