I just read a blog entry by a disgruntled self-published author who, after sending ARCs and final copies to review blogs only to see no significant increase in sales, concluded that all reviews are worthless. I'd have linked there, but given his tone, I don't think he's open to discussion and for all I know, he may show up here to start another "When self-published authors attack!" drama.
I'm writing this now because I love giving patronizing unwanted advice and I don't understand why that fellow doesn't seem to get this.
You see, if I am an author who has to pay for postage, et cetera, to send books to reviewers, here is what I would do.
First, I will decide whether the review site is worth my time and money. How do I know this? There are several ways to do this. One is by checking their website statistics, if available. Some, not all, websites openly display their statistics in hope of attracting advertisers. Another good way is to use Google and search for terms relevant to your books (example, "romance novel reviews", "romance reviews", "romance book reviews") and see which website shows up in the search results. Or if you want to be even more exact, pick a book by a popular author in your genre ("The Earl Who Ate A Carrot by Julia Quinn review") and see which websites show up in the Google search results. These websites are the ones indexed by Google, which means that these websites will ensure maximal exposure for the review of those books.
Google isn't everything, though. If we are talking about a blog (or if there is a forum), having an active community is also a good sign that the blog is well-read and well-trafficked. The thing here is, you need to spend some time looking over the comments - if the community comprise mostly authors, for example, chances are you won't find the readers you are looking for there. You want a community of readers who actively buy books to read the review of your book, remember that.
This is why I'd personally ditch all those blogs or websites that have a large amount of content targeted at authors - chances are, readers rarely go there, and you won't make any sales there. Also, this may seem heartless, but life is life, so I would also ditch smaller or new websites/blogs that haven't proven themselves. At the very least, I'd send them an electronic ARC instead of an actual book, and if they don't want that, well, it's too bad.
Of course, this puts self-published authors in a fix, since many places don't accept their books for review in any format, but let's look at it this way. Reviews don't really move a book as much as book critics would like you to believe. It's word of mouth that makes or breaks your book - when Oprah tells everyone to buy a book, that is word of mouth in action at its most potent form. Perhaps a self-published author has better spend time and money in distributing and displaying books in venues that will move those books better (local bookstores, trade fairs, et cetera)?
Getting your reviews in sixteen small blogs, all trafficked by authors desperate to get their books reviewed with only a small fraction of actual readers, is probably a waste of time and money. It's like advertising - you spend your money hoping to hit the best conversion rate - you want your review, the "ad", to be read by as many book-buying readers as possible. This principle should also be applied to review sites. Like publishers, not all review sites are created equal. Start from the top and work your way down. Don't settle for a small Blogspot or Wordpress blog with traffic of dubious quality and quantity if you feel that your ARCs and money are limited - aim for the big boys.