So if you bought the whole company at a $50b valuation, and assume that this $355m/yr profit rate for first 9 months held constant and therefore turned into $473m total by end of year, and then that rate held constant each year on forward, and that all profits were always and evenly distributed to all shareholders, then you'd recoup your investment (merely break even, anyway) after 105 years.

Add in an unpredictable future growth rate. Add in the fact that they're probably approaching a hard cap on users in the next year or so. Add in bubble-ishness. Add in a big unknown as to whether they find ways to better monetize their users. And all this adds up to telling me either this is a bad investment, or, maybe just maybe it will at least break even within your lifetime. Can't say. But from this data I think it is not clear that this is a slam dunk buy at all. Either bad or meh.