Competitor description from HTML comment

What is the good/bad of doing this?

[Storyman]

I've been helping a friend with his web site that is in competitive field--real estate. Tonight he asked how a site that has a single page, 8 bulleted lines of text, and a simple headline, achieved a top ten listing in Google.

There are no links to the page. The domain name was first registered 7 years ago, so I'm thinking time might be a factor.

The code shows that the description used by Google is an HTML comment in the header listed before the title tag.

Is this a good thing to do? What are the pros and cons?