If $US 810^8 (from http://economictimes.indiatimes.com/infotech/internet/Facebook-09-revenue-neared-800-mn-Sources/articleshow/6063819.cms http://economictimes.

If $US 810^8 (from http://economictimes.indiatimes.com/infotech/internet/Facebook-09-revenue-neared-800-mn-Sources/articleshow/6063819.cms http://economictimes.indiatimes.com/infotech/internet/Facebo...) is a good estimate of Facebook's revenue, then, assuming fairly stable advertising income (a reasonable assumption, as Facebook has a market share nearing saturation, and the market in social networking is mainstream enough that it probably won't grow too much), a valuation of $US510^10 is 62.5 years of growth. Facebook's brand has a lot of valuable goodwill, but they are still vulnerable to competition, and might not last 62.5 years - so the valuation seems way too high.