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Blogs continue to sell — but blog valuations are staying modest. Discovery Communications, the cable-and-online media company, has bought enviro blog TreeHugger for a reported $10 million. With nearly 2 million unique visitors, that means Discovery paid a very modest $5 per "eyeball" — the unpleasant online-advertising slang for a reader. Contrast that to the bubbly hopes of GigaOm's Om Malik back in 2005, when he wrote about the "return of monetized eyeballs" for Business 2.0. (Full disclosure: I helped him crunch the numbers for that story.)

If anything, TreeHugger's sale marks a steady downward trend from the frothy days of 2004 and 2005, when the $519 million deal Dow Jones struck to acquire MarketWatch and the $25 million sale of Jason Calacanis's Weblogs Inc. to AOL sparked hopes of pricier blog buyouts to come. But they didn't materialize.

Instead, today, blogs like TreeHugger are evaluated more like conventional media properties, based on audience size, advertising, and growth rates, not eyeballs alone. And, of course, strategic fit matters. Discovery's TV viewers are naturally drawn to green blogs. Better for Discovery to own those blogs than let its cable audience drift away to them.

(Update: Valleywag is owned by Gawker Media, and Gawker's publisher, Nick Denton, is an investor in and advisor to TreeHugger.)