Tehran is erupting in violence. The picture with the crowd is allegedly Mousavi addressing a rally today, where at some point, he allegedly told the crowd he is "ready for death."
There are reports of security forces firing into crowds and of helicopters spraying marchers with some kind of chemically treated water (looks like it may be CS tear gas crystals mixed in water) which makes the skin feel like it is scalding.
The best western site I have found to follow this is Andrew Sullivan's "The Daily Dish." This appears that if may turn into the first revolution ever twitterized. Seriously, regardless of what happens in Iran, Twitter has justified it's existence over the past week, as the majority of info coming out of Iran is the medium usually reserved for Lindsey Lohan telling us she just enjoyed asparagus carpacchio at Wolfgang's new Bistro.
Every Iranian expert I've managed to read yesterday and this morning has said today is the tipping point in Iran. If they powers that be fail to put these protesters down today, Iran's course may very well be altered. So check online tonight and see what happens.