That question can really only be answered by you.
But rather than get into a debate on the need or lack thereof right now, let's talk a little about what they are and some of the ways they can be use.
In the past, all you had to promote your book was a cover and a quick blurb/synopsis. That old saying "You can't judge a book by its cover," it's a bunch of bull!
People can and will judge your book by the cover. You could have a stellar write up and someone might still be turned off by the first image of it they see.
That's where a book trailer can help. Instead of only having a cover to present to people, you can also show them a visual representation of the blurb/summary.
Much like a movie trailer, this can help to tease the reader and entice them to take a chance on your work. Please note, I said can. There is no guarantee with book trailers.
Book trailers can be uploaded to a variety of places where people go to look for videos- Youtube being one of the most popular. This helps to give your trailer visibility. People love to watch online videos, right? With the right keywords your trailer could become a viral video. Again... "could." There is no guarantee with book trailers.
They can also be used as part of your marketing plan. Are you going on blog tour? Include the embed code for each of your stops. This way you get maximum exposure while traveling the blogosphere. People love to watch videos and they make a nice little way to finish up a guest post or interview.
Do you have a website for yourself or your novels? This should go without saying but...make sure the video is there too?
Post it on your social networking profiles as well.
Myspace
Goodreads
Amazon Author Central
Beyond that, there are also many sites dedicated to showcasing book trailers. If you have one, why not post it here?
Blazing Trailers
Book Trailer Matinee
Bookscreening
Preview the Book
Book Trailers
BookTrailers.ning
Now with all that said, I am sure you're chomping at the bit to get your book trailer made. But that brings us back to the original question of, do you really need one?
Book Trailers sound like the perfect marketing tool. Who wouldn't want to have one, right? Well, there is a small catch.
If you can't make a book trailer yourself, this can be a costly "tool" to create. And (I've said it before... I'll say it again) there is no guarantee that you will get any sales from a Book Trailer.
It's a tool. A very pretty tool, but it cannot make your book fly off of the shelves.
To make a book trailer you'll need some images, some music, and a nice little program to tie it all together. This can be accomplished using Windows Movie Maker or an online site like One True Media.
For my first trailer, I attempted to go it alone.
It's little more than a slide show, and some text with music. Not very flashy. Certainly not high-quality, but hey, it was free, right?
Now, compare that to one that was professionally done...
And you start to see why hiring out for this could be a better option. Let's face it, we're writers but that doesn't mean we are all artists.
Again I must state, there is no guarantee of added sales by having a book trailer. If you're thinking about hiring out for an artist to make your book trailer, you have to consider the cost. It's not going to be free. How much you want to dump into marketing?
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OK enough plugging, back on topic.
As I said before, these can be costly. I've seen book trailer creation sites out there with cost in the thousands and some with costs in the $10's. As with many things, you get what you pay for.
If you do want to go with something a little more polished and professional, consider these things:
Take a look at the previous trailers created by the site of your choice. Are they slide-show trailers? Are they animated? Are they actual movie clips?
The level of complexity in the trailers will affect their overall cost. If your marketing funds are low, you might want to look at places that create simpler trailers. Even a slide-show, if done right can look very nice.
Make sure that the person creating your trailer is really listening. Your trailer is a representation of your book. It needs to do a good job of that. And so does the person creating your trailer. Do they ask for summaries of your work to get a feel for the overall tone of the story? Do they make you an active part of locating the appropriate pictures? If your main character has blond hair, do you really want a brunette in your trailer? Communication with your artist is key.
Where do they get their photos? Pictures aren't free and many of the ones found online require rights to be purchased to use. Most trailer creation sites will use Royalty free stock photos and music. The cost of those photos are usually factored into the cost of the trailer. It's always best to be sure you know where your photos come from.
Do they allow for revisions? Nothing ever comes out perfect the first time. Does your book trailer creator give you the option to make "reasonable" changes or alterations to the product before it is finalized?
Again, you can do this yourself. It's a time consuming process that can be both frustrating and annoying. But, it can also be rewarding.
If, like me, you know your limitations but still desire to have this visual marketing tool, then do your homework and find a book trailer creator that is right for you.