Never judge a book by its cover.
Sounds like good advice, for both books and most other things, and yet it's also highly misleading for authors/readers. We do judge books by their covers. In fact, one of my reviews specifically stated that a part of the reason behind the chap buying it was because of the cover (and also title).
Judging a book by its cover is like judging someone by their appearance. We probably shouldn't do it, but the blonde girl wearing a bikini will get more attention than the unwashed fifty year old man swigging gin.
The title is similar. A rose by any other name would smell as sweet, but as The Simpsons suggested they'd probably be less popular if they were called crapweeds.
Tip for new authors: try and get the cover done much earlier than you think you'll need it. This'll ensure any issues with slow production or difficulty finding an artist won't delay the book's release.
Covers generally need to work in several ways. They need to look good full-size, but also as a thumbnail. Less important, but still helpful, is if they look good in black and white (for an eReader screen). A good cover can help gather more interest, which in turn leads to more purchases and hopefully reviews/word-of-mouth promotion.
By coincidence, after I wrote most of this but before I put it on the blog, I got an e-mail from a potential reviewer asking how gruesome Bane of Souls is (there are one or two grim bits but mostly it's not gruesome) because of the cover. Something for me to consider for future covers.
Personally I found the title of Bane of Souls trickier than the cover idea. You don't want to spoil your plot with the title, and at the same time it's best to be distinctive whilst making it plain the sort of thing that can be expected.
Tip for new authors: try and avoid very generic terms as titles. Otherwise, when people try searching for your work they'll get a massive list of results and may have difficulty finding your book.
Finding an artist did take me a while, but I was lucky to get one whose work I not only really like but whom I get along with very well too. (Lee Yoong, whose work can be found here: http://leeyoong.deviantart.com ). I searched Deviant Art, and there are lots of good artists on there (when asking about commissioning a piece check and, if necessary, ask to ensure they do commercial work. Otherwise you might get far down the track only for the artist to realise it's commercial and for them to reluctantly stop work on it, wasting your time and theirs).
Happily, artists tend to be rather more prompt than agents when accepting or rejecting work. Of the ones who got back to me, just about all of them did so within a week (and most within a day or two).
The cover and title are superficial compared to a hundred thousand words, but they're also far more noticeable and can be key to making potential readers into actual ones.