You’ve probably read(and experienced) a lot on how Google penalizes websites/blogs for duplicate content.
Whats that? You say your content is 100% unique and home-made? Well, thats not the utter and complete truth, because google indexes your content from http://yoursite.com and http://www.yoursite.com, effectively crawling your blog/website twice. This also dilutes the effectiveness or incoming links as some may point to the www version and others to the non-www version of your website.
Now you might think that the Googlebot isnt so dumb, and it isnt, but all the same its best to fix the problem.
Thats where the enforce www plugin comes in. From the page:
This plugin will help preserve your permalinks by enforcing your no-www or yes-www preference (http://example.com/ vs. http://www.example.com/) and will strip off index.php from the ends of URLs.
Once you’ve installed the plugin, set up your preference for your domain from Options->General tab on your WordPress admin menu, and thats all there is.
I use the non-www preference for Shypy.com, so even though you type in www.shypy.com in your browser, it always takes you to http://shypy.com (no WWW!) 
Edit: The same effect can be achieved by doing a .htaccess rewrite – more info can be found here
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I thought this plugin was really interesting too and almost installed it to make it switch to without the www since I’m always writing my URL without the www since a while back.
But: I recently happened to get some DNS-problems(?) and suddenly people couldn’t reach my site without the www. It still happens some time, for unknown reason.
So now I can’t decide if I really want to be without the http://www…. OK, these things shouldn’t happen often, but still.
So I’ve to decide that first, before installing the plugin I think
Maybe this would be a good solution to automatically switch to the www instead and therefor avoiding these problems…
This is a must-have plugin, and prevents google from confusing between your backlinks. I’ve seen many people who have different page ranks on the www and non-www version of their websites which could’ve easily been prevented if they’d installed this. Even on my static websites, I use a mod rewrite to remove www from the URL.
Trust me, you want this and if you’re still having problems with it, I’d be glad to help
Oh, and thanks for stopping by.