I am getting ready to install it on my eCommerce website. I am new to WF, so I can't post links, but head over to SEOMoz's blog and read their writeup. The entry also has 100s of comments by SEO professionals.

Overall, it seems 50/50 among people. Half say you need to do it and cannot afford to be left behind, while the other says giving the search engines ever more information only makes them more powerful and you the web designer less.

I personally think it is a good thing and have heard that it really increases SERP click-through rates. For eCommerce, IMHO, it is a must have.