Several devoted Snarklings have written to ask if agents, specifically Miss Snark, surf the blogosphere. You bet. In her snark suit. With her snarkboard. Wearing heels. Cowabunga Snarklings.
Hard to tell who people "are" sometimes on a blog.
When you read Beatrice the blog by Ron Hogan are you reading the blog of a book reviewer, writer, reader, or hot shot cigar smoker?
Same for the inestimable Maud who is a writer, reader, reviewer and commentator on the world.
Or Jaimie who is both a writer and a phtographer and all around interesting character.
All sorts of established authors have blogs and I sniff around those periodically.
All sorts of people I don't know have blogs, and I sort of poke around in them.
Do I look for writers by reading their blogs? No
I find writers the old fashioned way: they fall into my mailbox with nice letters.
However, if someone queries me and says "Dearest Miss Snark, I have a blog that gets 1000 unique hits a day" and "my blog is about my writing" of course I'd pay attention.
Miss Snark, for all of her peculiar ways and fondness for gin, knows a marketing bonus when she sees it.
Now, is it a good idea to spend as much time on a blog as it would take to get 1000 unique hits a day?
Probably not. Better to spend it on your actual writing. A good blog with tons of hits won't sell a novel. Good writing will. A good blog might pump up the amount of money you can get for a good novel, but it's not going make a pig surf.