As you know, if you follow my blog, and only one person follows my blog, I don't update much.
I'm on FB more and I do tweet a few times a week, but I don't do online reviews or follow and comment on other blogs about writing/publishing/novels. Compared to a lot of other writers out there, I pretty much don't exist online. But I'm the one with the bigtimewriter deal and they are still trying to get their novel finished. I'm the one with the pre-order listing for my novel on various online booksellers like B&N, Amazon and Chapters, and their presence on these sites is their name at the bottom of the reviews they have written about someone else's book. I'm the one with the bigtimewriter hardcover book coming out on March 1, 2011 and they're not. I'm not saying having an online presence won't help you get published. But you also need a completed manuscript to send out to publishers or agents. If you don't have a complete manuscript, then it doesn't matter how much you blog, tweet or comment.
So my writer friend who would complain about no time to write but had time to blog? They finally completed their novel. And you know what? They sent it out and found a publisher.