Via a link on Dear Author, I just read Jason Pinter's question on whether an author having an online presence really helps to sell their books. It's a good question. The epublishing houses want their authors to have a marketing strategy, and this naturally means an online presence. So some people think it works.
There are tons of books out there. The big issue for readers is finding ones they enjoy. Sometimes we go with a publishing house. I know I buy particular Harlequin lines and lately have picked up a number of Ace urban fantasy. But really I rely on my experience with previous books by an author, and where a back history is not available, recommendations/reviews by authors I like will tempt me to try a new author. So I buy by author.
The question Jason Pinter raised was whether in buying by author, I'm influenced by how they present themselves online. Unfortunately for all the lovely author websites out there, the answer is no. I buy because I loved their previous books. Their websites make me aware of when a new book's coming out--but Amazon could fill the same function. I do feel guilty when I don't buy a book from a lovely author, but guilt doesn't add to their royalties.