I am asked this question on occasion (enough that I thought it was worth of a post) and feel I need to talk about a few things regarding this subject.
If you have a brand new site, and are trying to get the search engines to notice you and crawl you regularly setting up a blog could be a good thing if done correctly. You can’t just create a blog and do nothing with it for it to be effective. You need to be an acitve blogger, and post something atleast every 3 days (daily if possible). Make sure you are not posting about what you ate for breakfast either. You need to provide useful, unique content related to what your website is about (and make it worth reading!!)
When doing this you are creating what is called “spider food” for the crawlers. When you give them reasons to keep coming back and indexing your site they will. Most often, when your site is brand new, and you don’t have anything but products, and an about us page its good to have content from a blog that keeps it fresh. Think about it, your products (or services) have been added to your website, and that information is not going to change that often, so the spiders will not visit you as often as they would if you were blogging about topics related to your site.
Even if your site is older and you have content that does not change that often its good to start blogging to get the crawlers coming back to your site on a regular basis. it could help improve your rankings and turn into more traffic.