Al Jazeera puts the number protesting in downtown Cairo at over 2 million:
These are the latest pictures from Cairo's Tahrir Square where over two million people from all walks of live are protesting against Mubarak...Wow:
(Click images for larger version)Al Jazeera also notes that hundreds of thousands are marching in smaller cities across Egypt.
Of course, these are not official estimates, and the numbers may be revised downwards or upwards in the future.
Of course, these are not official estimates, and the numbers may be revised downwards or upwards in the future.