I'm interested in how agents would treat submissions from a blogging author? To explain further, I have had some success with two previously self-published works mainly due to my determination to exploit the marketing opportunities that have arisen as a result of the internet. Readers of my previous works are taking a keen interest in my newest project so I have posted some early draft chapters on a blog, asked for feedback, all to get them interested and engaged in the process. I have read so many varying opinions on how this would be considered by agents and publishers come submission time from: "if it helps sell more books then why not", to concerns over copyright and whether the ms would be deemed already published. I'm interested in your view on this.
I don't think there's one rule for this; it really depends on what you're writing about. If your content is amazing and can be adapted for a book, the blog should be no hindrance - and possibly no help either. But if the content isn't amazing then the blog won't help it become a book.
However ... I don't know if you're writing a novel or non-fiction. If it's a novel, I wouldn't advise you put the whole thing on the blog because then there's not as much reason for people to buy your book. If it's non-fiction, it's likely it will change form once it goes into a book. The trick is to not give away too much on the blog, for either type of manuscript, because presumably you want some of your blog readers to buy your book just as you want to capture a bigger readership.
As a general thing, I do believe it's important for authors to have a web presence, whether it's a blog or a standard website, but a blog is preferable because RSS feeds run on blogs and not on HTML sites. Plus, most blogs are free. The whole blog-to-book thing is still relatively new, though, so it's likely that what I've said above may not apply in a year's time. My own gut feeling is that it always comes down to the writing, regardless of where the writing comes from.