Yesterday Wilkipedia shut down their site for 24 hours,they did not loss any money but user suffered from this .

Here are some stats which tells how much lose other big company

Google: Google normally makes $3 billion a month from advertising only. Their main income is the text link ads you see in almost every site. So if they shut down they might be losing about $100 million per day.
Facebook: If they closed shop for one day they would lose almost $11.7 million and would loose tons of FB users.
Twitter: Twitter being the market place of all times, if they shut down, users will hardly have a place to spread their word. Twitter would lose around $400,000.
eBay: In 2010, eBay’s revenue was $9 billion. Calculating the predictions, eBay would lose $28 million in one day not taking the individual seller loses.
Amazon Amazon would have been looking at around $82 million lost in one day.
Yahoo: Even Yahoo will be losing 11.8 million a day but they have their own problems to worry about these days..