That isn't the point they're making here, though. They're comparing the valuation with the size of the user base. For example, at $3b for LinkedIn, divided by the number of users they have, it comes to about $33.33 per user. In other words, a sort of very rough market valuation of what the industry thinks the users are worth, I suppose.

It is, but the above list is per user, not per share, which certainly has meaning.

Not totally meaningless, but certainly it doesn't tell you the value of the company unless you know how many shares exist.

However, the comment you replied to isn't about stock prices, it's about the value of each user for each of those companies - user as in somebody who uses those services.