I'm sitting in my car when I see a magazine salesman coming up to the window, trying to sell me a copy of "Good Housekeeping". Another of their lot was trying to sell a copy of "Maxim" to my mother.
We didn't buy either. There was nothing wrong with the products; both are excellent, world-class products (I can certainly vouch for Maxim ;) though I'm not too sure about Good Housekeeping).
This is what happens when you've got a great product but you don't identify a target audience: no sales. Period. Marketing your product is thus as important as having a great product. Maybe even more important.
Contrary to popular belief, Marketing is not just about making awesome ads. The first step is to find a target audience and then create a campaign that will convince it. Just having a great campaign probably won't result in a sale either (unless the customer is an idiot).
You can't sell a garage-lock to a guy that doesn't have a garage, even if you've convinced him that you have the finest garage-lock in the market.
Take a look at some successful products around you. Most of them have done well because the marketers identified a target audience and worked to sell it to that very audience by developing a great sales pitch.
This applies as much in the online world as it does offline. Websites (blogs included) have to identify a target audience and sell themselves to it. Of course, this stage comes only after you have something worth selling (please note that I am not using the word sell literally). For a website that something is either great/unique/quality content or a great services.
The reason that most blogs (mine included) aren't too popular is because:-
1. they don't have anything unique (most are personal blogs)
2. they don't have great content in addition to being non-unique
3. they don't have a target audience
Who are you writing for? Why should people read your blog/website? Will it make any conceivable difference to them if they didn't read it?
The answers to these questions most often are: dunno, dunno and no (these are also my own answers). And the result is obvious.

P.S. I have no idea why I wrote this. It's a strange post, admittedly, but quite relevant to most bloggers. And I'm not writing this to discourage anyone from blogging. And yes, I have written a rather meandering post where I've been moving back and fort between marketing, target audiences and great products.