So do these companies make actual money or they just have revenue?
callmeed: I don't mean nitpick your title, but "revenue" is "making money" (actual money, even).When the company is public (or acquired by a public company) you can usually find out if they're profitable.For example, YouTube is not profitable. It generates revenue via advertising but not enough to cover its costs. 
http://rochakchauhan.com/blog/2008/08/09/youtube-not-profita...Skype, it appears, is a profitable venture for eBay. Search "skype profitable" and you'll find that it has been since '07.Because Facebook is a private company, you'll find less specifics about their revenue and profit. My understanding, however, is that they're not profitable yet. IIRC Marc Andreessen told Charlie Rose that they could be profitable if they put ads on the home page.I don't know enough about the other ...