1. You'll find other sites that link to you organically will almost always use the www. version. Virtually every site's www. PR is equal to, or higher than, the non-www version.

2. When you post your domain in forums, blogs or email applications they automatically convert the URL to a clickable link, not only making it much easier for people to click/visit your site, it also creates a link to your site for SE spiders to follow.

As yourself this, which of the following URLs are more likely to get you to visit my site?

Which one will the SE spiders follow?

Tuelz.com
www.Tuelz.com

While the "www" may not affect the engines directly, we can see in the example above that using the www is not only SE friendly, it is people friendly.