With all the talk about a Vonage IPO and its valuation, some people have turned their investment sights on Skype. One estimate by Eurotelcoblog values Skype at US$130-million, or about US$130 per SkypeOut user. I love these type of exercises because you can use whatever metrics and valuations you want to come up with a final number. Given Skype is private and less than forthcoming about its financials, it is difficult to get an accurate idea of Skype's real value. That said, a company is worth whatever someone's willing to pay for it. How much is 100 million Skype downloads or 31 million registered users worth? $1 a download, $10 a download, $5 a registered user. I think the mystery surrounding the valuations of privately-owned companies is what's keeping Vonage on the IPO sidelines. By not revealing everything about yourself, it builds the suspense before someone take the plunge.