As with the protests in Tunisia throughout the last month (which at least partially inspired the Egyptian uprising), the protest in Cairo was organized using Facebook. The Christian Science Monitor reports that more than 90,000 people signed up on a Facebook Page for the protests in the past week, though the turnout appears to be much smaller than that.
Another similarity between the Egyptian protests and the Tunisia uprising: People on the ground have been using Twitter to post photos, video feeds and other information about the protests using hashtags like #Jan25, #EgyRevolt and #Egypt.
But now some reports indicate that Twitter as well as some websites reporting live on the demonstrations have been blocked in Egypt. Vodafone Egypt also confirms that Twitter is down in this tweet.
We have reached out to Twitter for confirmation and will be updating this article as we hear more.