[shadaik]

I'd like to second Elfwreck and add a little something:

The blurb you put in your book promo and your postings in these boards in general give people an impression of the way you think, talk/write and argue. How you describe and express yourself. The qualities that make a good author.
Be notable in writing on here (and elsewhere) and people will start to take an interest in your book writing as well.

Not only are the people on here often avid readers, more likely to buy or at least check out a book promoted by you. There also outspoken, as evidenced by them writing posts on these boards. Meaning if they like the book, there is some chance they will tell others. And being known as avid readers, their recommendations often count double.

You don't just get a few readers here. You get the best quality brand of readers: Actively interested ones who are more likely than average to spread the word about your book further, if they like it.
There is absolutely nothing in marketing that beats successfully establishing promotion by honest word of mouth.